Compositions, methods, and systems to form vaterite with magnesium oxide

ABSTRACT

Provided herein are compositions, methods, and systems comprising vaterite and magnesium oxide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/723,718, filed Apr. 19, 2022, issued as U.S. Pat. No. 11,530,164 onDec. 20, 2022, which claims benefit of U.S. Provisional Application No.63/176,709 filed Apr. 19, 2021, which are incorporated herein byreference in their entirety in the present disclosure.

BACKGROUND

Carbon dioxide (CO₂) emissions have been identified as a majorcontributor to the phenomenon of global warming. CO₂ is a by-product ofcombustion, and it creates operational, economical, and environmentalproblems. It may be expected that elevated atmospheric concentrations ofCO₂ and other greenhouse gases can facilitate greater storage of heatwithin the atmosphere leading to enhanced surface temperatures and rapidclimate change. In addition, elevated levels of CO₂ in the atmospheremay also further acidify the world's oceans due to the dissolution ofCO₂ and formation of carbonic acid. The impact of climate change andocean acidification would be economically expensive and environmentallyhazardous if not timely handled. Reducing potential risks of climatechange requires sequestration and avoidance of CO₂ from variousanthropogenic processes.

SUMMARY

Provided herein are methods and systems that relate to capturing the CO₂emissions and producing compositions with unique properties that can beused to make cementitious or non-cementitious products.

In one aspect, there is provided cement or non-cement composition,comprising: vaterite and magnesium oxide. In some embodiments of theaforementioned aspect, the vaterite is between about 30-99 wt % andmagnesium oxide is between about 1-70 wt %. In some embodiments of theaforementioned aspect and embodiments, the particle size of the vateriteis between about 0.1-100 micron. In some embodiments of theaforementioned aspect and embodiments, the composition is a dry powdercomposition. In some embodiments of the aforementioned aspect andembodiments, the composition is wet cake composition or is slurry. Insome embodiments of the aforementioned aspect and embodiments, themagnesium oxide is under burnt magnesium oxide, soft burnt magnesiumoxide, dead burnt magnesium oxide, or combination thereof. In someembodiments of the aforementioned aspect and embodiments, the vateriteis partially on surface of the magnesium oxide. In some embodiments ofthe aforementioned aspect and embodiments, the composition furthercomprises admixture, aggregate, additive, Portland cement clinker,supplementary cementitious material (SCM), or combination thereof.

In some embodiments of the aforementioned aspect and embodiments, thecomposition further comprises aragonite, calcite, magnesium hydroxide,or combination thereof, and water, wherein the composition is a slurrycomposition. In one aspect, there is provided cement or non-cementslurry composition comprising vaterite, aragonite, calcite, magnesiumoxide, magnesium hydroxide, or combination thereof, and water. In someembodiments of the aforementioned aspect, the vaterite transforms to thearagonite and/or the calcite upon dissolution and re-precipitation inwater and the magnesium oxide transforms to the magnesium hydroxide. Insome embodiments of the aforementioned aspect and embodiments, thearagonite is in shape of network of needles. In some embodiments of theaforementioned aspect and embodiments, the magnesium hydroxide binds thearagonite needles together. In some embodiments of the aforementionedaspect and embodiments, the magnesium hydroxide binds the calcitetogether. In some embodiments of the aforementioned aspect andembodiments, the magnesium hydroxide stabilizes the aragonite andprevents its transformation to calcite. In some embodiments of theaforementioned aspect and embodiments, the water is bound to thecomposition in form of the magnesium hydroxide. In some embodiments ofthe aforementioned aspect and embodiments, the composition has a pH ofabove 10. In some embodiments of the aforementioned aspect andembodiments, the composition further comprises admixture, aggregate,additive, Portland cement clinker, supplementary cementitious material(SCM), or combination thereof.

In one aspect, there is provided cement or non-cement product comprisingaragonite and/or calcite, and magnesium hydroxide wherein the magnesiumhydroxide binds the aragonite and/or the calcite together. In someembodiments of the aforementioned aspect, the product has between 0-95%porosity. In some embodiments of the aforementioned aspect andembodiments, the product has compressive strength of more than 0.05 MPa.In some embodiments of the aforementioned aspect and embodiments, theproduct has a pH of above 10 and prevents steel corrosion. In someembodiments of the aforementioned aspect and embodiments, the aragoniteis in shape of network of needles. In some embodiments of theaforementioned aspect and embodiments, the magnesium hydroxide binds thearagonite and/or the calcite together. In some embodiments of theaforementioned aspect and embodiments, the magnesium hydroxide fillsporosity of the aragonite and/or the calcite making it dense and lessporous. In some embodiments of the aforementioned aspect andembodiments, the magnesium hydroxide stabilizes the aragonite andprevents its transformation to calcite.

In one aspect, there are provided methods to form a composition,comprising:

(i) calcining limestone to form a mixture comprising lime and magnesiumoxide, and a gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in aN-containing salt solution to produce an aqueous solution comprisingcalcium salt and magnesium oxide; and

(iii) treating the aqueous solution comprising calcium salt andmagnesium oxide with the gaseous stream comprising carbon dioxide toform a composition comprising vaterite and magnesium oxide.

In some embodiments of the aforementioned aspect, the method furthercomprises producing a solid comprising magnesium oxide in step (ii) andtreating the aqueous solution comprising calcium salt and magnesiumoxide and the solid comprising magnesium oxide with the gaseous streamcomprising carbon dioxide to form the composition comprising vaterite,magnesium oxide, and solid comprising magnesium oxide.

In one aspect, there are provided methods to form a composition,comprising:

(i) calcining limestone to form a mixture comprising lime and magnesiumoxide, and a gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in aN-containing salt solution to produce an aqueous solution comprisingcalcium salt and a solid comprising magnesium oxide;

(iii) separating the solid from the aqueous solution;

(iv) treating the aqueous solution comprising calcium salt with thegaseous stream comprising carbon dioxide to form a compositioncomprising vaterite; and

(v) mixing the composition comprising vaterite and the solid comprisingmagnesium oxide.

In one aspect, there are provided methods to form a composition,comprising:

(i) calcining limestone to form a mixture comprising lime and magnesiumoxide, and a gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide, in anaqueous N-containing salt solution to produce a first aqueous solutioncomprising calcium salt and magnesium oxide, and a gaseous streamcomprising ammonia;

(iii) recovering the gaseous stream comprising carbon dioxide and thegaseous stream comprising ammonia and subjecting the gaseous streams toa cooling process to condense a second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, ammonia carbamate, orcombinations thereof; and

(iv) treating the first aqueous solution comprising calcium salt andmagnesium oxide with the second aqueous solution comprising ammoniumbicarbonate, ammonium carbonate, ammonia, ammonia carbamate, orcombinations thereof to form a composition comprising vaterite andmagnesium oxide.

In some embodiments of the aforementioned aspect, the method furthercomprises producing a solid comprising magnesium oxide in step (ii) andtreating the first aqueous solution comprising calcium salt andmagnesium oxide and the solid comprising magnesium oxide with the secondaqueous solution to form the composition comprising vaterite, magnesiumoxide, and solid comprising magnesium oxide.

In one aspect, there are provided methods to form a composition,comprising:

(i) calcining limestone to form a mixture comprising lime and magnesiumoxide, and a gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide, in anaqueous N-containing salt solution to produce a first aqueous solutioncomprising calcium salt, a solid comprising magnesium oxide, and agaseous stream comprising ammonia;

(iii) separating the solid from the first aqueous solution;

(iv) recovering the gaseous stream comprising carbon dioxide and thegaseous stream comprising ammonia and subjecting the gaseous streams toa cooling process to condense a second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, ammonia carbamate, orcombinations thereof;

(v) treating the first aqueous solution comprising calcium salt with thesecond aqueous solution comprising ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonia carbamate, or combinations thereof to form acomposition comprising vaterite; and

(vi) mixing the composition comprising vaterite and the solid comprisingmagnesium oxide.

In some embodiments of the foregoing aspects, the limestone comprisesbetween about 1-70% magnesium or magnesium bearing mineral. In someembodiments of the foregoing aspects and embodiments, the methodsfurther comprise mixing a magnesium bearing mineral with the limestonebefore the calcination. In some embodiments of the foregoing aspects andembodiments, the magnesium bearing mineral comprises between about 1-70%magnesium. In some embodiments of the foregoing aspects and embodiments,the magnesium or magnesium bearing mineral upon the calcination formsthe magnesium oxide. In some embodiments of the foregoing aspects andembodiments, the magnesium bearing mineral comprises magnesiumcarbonate, calcium magnesium carbonate, magnesium salt, potassiummagnesium salt, magnesium hydroxide, magnesium silicate, magnesium ironsilicate, magnesium sulfate, or combination thereof. In some embodimentsof the foregoing aspects and embodiments, the magnesium bearing mineralcomprises magnesium carbonate, magnesium salt, magnesium hydroxide,magnesium silicate, magnesium sulfate, or combination thereof. In someembodiments of the foregoing aspects and embodiments, the magnesiumbearing mineral is selected from the group consisting of dolomite,magnesite, brucite, carnallite, talc, olivine, artinite, hydromagnesite,dypingite, barringonite, liesquehonite, lansfordite, kieserite, andcombination thereof.

In some embodiments of the foregoing aspects and embodiments, thecalcining produces a mixture comprising under burnt lime, soft burntlime, dead burnt lime, under burnt magnesium oxide, soft burnt magnesiumoxide, dead burnt magnesium oxide, or combination thereof. In someembodiments of the foregoing aspects and embodiments, the methodsfurther comprise controlling the calcination process to controlcomponents of the mixture. In some embodiments of the foregoing aspectsand embodiments, the controlling the calcination process comprisescontrolling temperature and/or duration of heating of the limestone.

In some embodiments of the foregoing aspects and embodiments, themethods further comprise transforming the vaterite to aragonite and/orcalcite upon dissolution and re-precipitation in water and transformingthe magnesium oxide to magnesium hydroxide. In some embodiments of theforegoing aspects and embodiments, the methods further comprise formingthe aragonite in needle shape. In some embodiments of the foregoingaspects and embodiments, the methods further comprise binding thearagonite and/or the calcite together with the magnesium hydroxide. Insome embodiments of the foregoing aspects and embodiments, the methodsfurther comprise stabilizing the aragonite with the magnesium hydroxideand preventing its transformation to calcite. In some embodiments of theforegoing aspects and embodiments, the methods further comprise formingthe composition with a pH of above 10. In some embodiments of theforegoing aspects and embodiments, the methods further comprise bindingwater to the composition in form of the magnesium hydroxide therebypreventing unbound water in the composition.

In some embodiments of the foregoing aspects and embodiments, themethods further comprise setting and hardening of the aragonite and/orthe calcite and forming a cement product. In some embodiments of theforegoing aspects and embodiments, the methods further comprise fillingporosity of the aragonite and/or the calcite with the magnesiumhydroxide making it dense and less porous. In some embodiments of theforegoing aspects and embodiments, the methods further comprisepreventing transformation of the aragonite to the calcite due to thepresence of the magnesium hydroxide.

In some embodiments of the foregoing aspects and embodiments, theN-containing salt is selected from the group consisting of N-containinginorganic salt, N-containing organic salt, and combination thereof. Insome embodiments of the foregoing aspects and embodiments, thecalcination is carried out in shaft kiln, rotary kiln, or electric kiln.In some embodiments of the foregoing aspects and embodiments, theN-containing inorganic salt is selected from the group consisting ofammonium halide, ammonium acetate, ammonium sulfate, ammonium sulfite,ammonium nitrate, ammonium nitrite, and combination thereof. In someembodiments of the foregoing aspects and embodiments, the ammoniumhalide is ammonium chloride.

In some embodiments of the foregoing aspects and embodiments, theaqueous solution or the first aqueous solution further comprises ammoniaand/or N-containing salt.

In some embodiments of the foregoing aspects and embodiments, molarratio of the N-containing salt:the mixture comprising lime and magnesiumoxide is between about 0.5:1-3:1.

In some embodiments of the foregoing aspects and embodiments, thedissolving step is under one or more dissolution conditions selectedfrom the group consisting of temperature between about 30-200° C.;pressure between about 0.1-10 atm; the N-containing salt wt % in waterbetween about 0.5-50%; and combination thereof.

In some embodiments of the foregoing aspects and embodiments, noexternal source of carbon dioxide and/or ammonia is used and the processis a closed loop process.

In some embodiments of the foregoing aspects and embodiments, thegaseous stream comprising ammonia further comprises water vapor.

In some embodiments of the foregoing aspects and embodiments, thegaseous stream further comprises between about 20-90% water vapor.

In some embodiments of the foregoing aspects and embodiments, noexternal water is added to the cooling process.

In some embodiments of the foregoing aspects and embodiments, thecooling step is under one or more cooling conditions comprisingtemperature between about 0-100° C.; pressure between about 0.5-50 atm;pH of the aqueous solution between about 8-12; flow rate of the CO₂;ratio of CO₂:NH₃ between about 0.1:1-20:1; or combination thereof.

In some embodiments of the foregoing aspects and embodiments, the secondaqueous solution is formed by the condensation of the gases.

In some embodiments of the foregoing aspects and embodiments, thetreating step is under one or more precipitation conditions selectedfrom the group consisting of pH of the aqueous solution or the firstaqueous solution of between 7-9, temperature of the solution between20-60° C., residence time of between 5-60 minutes, or combinationthereof.

In some embodiments of the foregoing aspects and embodiments where thesolid comprising magnesium oxide is formed, the solid further comprisessilicate, iron oxide, alumina, or combination thereof. In someembodiments of the foregoing aspects and embodiments, the solids arebetween 1-40 wt % in the aqueous solution or the first aqueous solution,in the composition, or combinations thereof.

In some embodiments of the foregoing aspects and embodiments, themethods further comprise separating the solids from the aqueous solutionor the first aqueous solution before the treatment step by filtrationand/or centrifugation. In some embodiments of the foregoing aspects andembodiments, the separated solids are added back to the composition asfiller.

In some embodiments of the foregoing aspects and embodiments, theseparated solids further comprise residual ammonium halide when theN-containing inorganic salt is the ammonium halide.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises recovering the residual ammonium halide from thesolids using a recovery process selected from the group consisting ofrinsing, thermal decomposition, pH adjustment, and combination thereof.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises dewatering the precipitation material/composition toseparate the composition from the supernatant solution.

In some embodiments of the foregoing aspects and embodiments, thecomposition and the supernatant solution comprise residual N-containingsalt.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises removing and optionally recovering ammonia and/orN-containing inorganic salt from the residual N-containing inorganicsalt comprising removing and optionally recovering the residualN-containing inorganic salt from the supernatant aqueous solution and/orremoving and optionally recovering the residual N-containing inorganicsalt from the precipitation material/composition.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises recovering the residual N-containing inorganic saltfrom the supernatant aqueous solution using recovery process selectedfrom the group consisting of thermal decomposition, pH adjustment,reverse osmosis, multi-stage flash distillation, multi-effectdistillation, vapor recompression, distillation, and combinationthereof.

In some embodiments of the foregoing aspects and embodiments, the stepof removing and optionally recovering the residual N-containinginorganic salt from the precipitation material/composition comprisesheating the composition between about 300-360° C. to evaporate theN-containing inorganic salt from the composition with optional recoveryby condensation of the N-containing inorganic salt.

In some embodiments of the foregoing aspects and embodiments, theN-containing inorganic salt is ammonium chloride which evaporates fromthe composition in a form comprising ammonia gas, hydrogen chloride gas,chlorine gas, or combinations thereof.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises recycling the recovered residual ammonia and/orN-containing inorganic salt back to the dissolving and/or treating stepof the process.

In some embodiments of the foregoing aspects and embodiments, thearagonite and/or the calcite sets and hardens to form the cementitiousproduct selected from masonry unit, construction panel, conduit, basin,beam, column, slab, acoustic barrier, insulation material, andcombination thereof.

In some embodiments of the foregoing aspects and embodiments, thearagonite and/or the calcite sets and hardens to form thenon-cementitious product.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises adding an additive to the aqueous solution, to thefirst aqueous solution, and/or to the composition, wherein the additiveis selected from the group consisting of fatty acid ester, sodium decylsulfate, lauric acid, sodium salt of lauric acid, urea, citric acid,sodium salt of citric acid, phthalic acid, sodium salt of phthalic acid,taurine, creatine, dextrose, poly(n-vinyl-1-pyrrolidone), aspartic acid,sodium salt of aspartic acid, magnesium chloride, acetic acid, sodiumsalt of acetic acid, glutamic acid, sodium salt of glutamic acid,strontium chloride, gypsum, lithium chloride, sodium chloride, glycine,sodium citrate dehydrate, sodium bicarbonate, magnesium sulfate,magnesium acetate, sodium polystyrene, sodium dodecylsulfonate,poly-vinyl alcohol, and combination thereof.

In some embodiments of the foregoing aspects and embodiments, thevaterite is unimodal, bimodal, or multimodal distribution of aparticulate composition with an average particle size of between about0.1-100 micron.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises blending the composition with Ordinary Portland Cement(OPC), aggregate, limestone, or combination thereof.

In some embodiments of the foregoing aspects and embodiments, the methodfurther comprises mixing the composition with an admixture selected fromthe group consisting of set accelerator, set retarder, air-entrainingagent, foaming agent, defoamer, alkali-reactivity reducer, bondingadmixture, dispersant, coloring admixture, corrosion inhibitor,damp-proofing admixture, gas former, permeability reducer, pumping aid,shrinkage compensation admixture, fungicidal admixture, germicidaladmixture, insecticidal admixture, rheology modifying agent, finelydivided mineral admixture, pozzolan, aggregate, wetting agent, strengthenhancing agent, water repellent, reinforced material, and combinationthereof.

In some embodiments of the foregoing aspects and embodiments, thereinforced material is a fiber made of zirconia, aluminum, glass, steel,carbon, ceramic, grass, bamboo, wood, fiberglass, synthetic material, orcombination thereof.

In one aspect, there is provided a product formed by the methodsaccording to the aforementioned aspects and the embodiments.

In one aspect, there are provided systems to form a composition,comprising:

(i) a calcining reactor configured to calcine limestone to form amixture comprising lime and magnesium oxide, and a gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in an aqueous N-containing salt solution to produce an aqueoussolution comprising calcium salt and magnesium oxide; and

(iii) a treatment reactor operably connected to the dissolution reactorand the calcination reactor configured for treating the aqueous solutioncomprising calcium salt and magnesium oxide with the gaseous streamcomprising carbon dioxide to form a composition comprising vaterite andmagnesium oxide.

In one aspect, there are provided systems to form a composition,comprising:

(i) a calcining reactor configured to calcine limestone to form amixture comprising lime and magnesium oxide, and a gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in an aqueous N-containing salt solution to produce a firstaqueous solution comprising calcium salt and magnesium oxide, and agaseous stream comprising ammonia;

(iii) a cooling reactor operably connected to the dissolution reactorand the calcination reactor configured for recovering the gaseous streamcomprising carbon dioxide and the gaseous stream comprising ammonia andsubjecting the gaseous streams to a cooling process to condense a secondaqueous solution comprising ammonium bicarbonate, ammonium carbonate,ammonia, ammonium carbamate, or combinations thereof; and

(iv) a treatment reactor operably connected to the dissolution reactorand the cooling reactor configured for treating the first aqueoussolution comprising calcium salt and magnesium oxide with the secondaqueous solution comprising ammonium bicarbonate, ammonium carbonate,ammonia, ammonium carbamate, or combinations thereof to form acomposition comprising vaterite and magnesium oxide.

In some embodiments of the foregoing aspects, the dissolution reactor isintegrated with the cooling reactor.

DRAWINGS

The features of the invention are set forth with particularity in theappended claims. A better understanding of the features and advantagesof the invention will be obtained by reference to the following detaileddescription that sets forth illustrative embodiments, in which theprinciples of the invention are utilized, and the accompanying drawingsof which:

FIG. 1 illustrates some embodiments of the methods and systems providedherein.

FIG. 2 illustrates some embodiments of the methods and systems providedherein.

FIG. 3 illustrates some embodiments of the methods and systems providedherein.

FIG. 4 illustrates some embodiments of the methods and systemscomprising an integrated reactor provided herein.

FIG. 5 illustrates a Gibbs free energy diagram of the transition fromthe vaterite to the aragonite.

FIG. 6A and FIG. 6B illustrate scanned electron microscope images ofcalcium carbonate cement containing the aragonite made from the vateriteat 1000× magnification (FIG. 6A) and 2500× magnification (FIG. 6B).

FIG. 7A and FIG. 7B illustrate scanned electron microscope images ofcalcium carbonate cement containing the aragonite and the magnesiumhydroxide made from the vaterite and the magnesium oxide, respectively,at 1000× magnification (FIG. 7A) and 2500× magnification (FIG. 7B).

DESCRIPTION

Transformation of the calcium carbonate cement may not chemically bindwater; therefore, whatever water is used to make the calcium carbonatecement paste, mortar, or concrete, may remain in the cement after thetransformation. The remaining water, after evaporation, may contributeto porosity of the calcium carbonate cement paste and negatively affectthe hardened cement paste's strength, hardness, and durability. Further,the transformation from the vaterite to either the calcite or thearagonite may result in a decrease in solid volume which may furtherincrease the porosity of the cement, creating durability and strengthchallenges of the cemented composite.

Applicants have found unique compositions, methods, and systemscomprising vaterite and magnesium oxide (MgO) that obviate thesechallenges and provide durable aragonite cement composite and/or calcitecement composite with high compressive strength. It was unexpectedlyfound that the transformation of the vaterite to the aragonite and/orthe calcite and the magnesium oxide to the magnesium hydroxide, afterthe dissolution and re-precipitation with water, forms the aragoniticcement and/or the calcitic cement bound to the magnesium hydroxide thathas high durability and strength.

Incorporating the magnesium oxide (e.g., periclase) into the vateritecomposition may provide one or more of the following advantages. First,the magnesium oxide in the composition comprising the vaterite canprovide the magnesium ions necessary to control the transformation ofthe vaterite into the aragonite (optionally preventing furthertransformation to the calcite) and/or to the calcite. Second, themagnesium oxide may chemically react with the water to form themagnesium hydroxide. The bound water then may add to the hardened cementpaste's volume, thereby reducing the cement paste's porosity. Thedecrease in porosity may result in increase in strength, hardness, anddurability. Third, the presence of the magnesium hydroxide may bufferthe pH of the cement's pore solution to approximately more than 9, whichmay be sufficient to prevent mild steel reinforcement from activelycorroding in the cement structures.

Accordingly, provided herein are unique compositions, methods, andsystems, comprising the vaterite and the magnesium oxide formed from thelimestone which can be used to form various products as describedherein. The limestone is calcined to form lime which is treated with anaqueous N-containing salt solution, such as for example only, ammoniumsalt e.g., aqueous ammonium chloride solution or ammonium acetatesolution, to solubilize or dissolve calcium of the lime in an aqueoussolution. The magnesium oxide may be formed from the minerals in thelimestone during calcination; may be formed from any magnesium bearingmineral separately added to the limestone during calcination; and/or maybe added to the composition comprising the vaterite after its formation.All of these methods are well within the scope of the invention and oneor more of these methods may be combined to achieve the compositions,methods, and systems provided herein. The dissolved calcium in the formof calcium salt is then treated with the carbon dioxide gas (e.g., CO₂evolved during the calcination of the limestone) to form theprecipitation material/composition comprising the vaterite and themagnesium oxide.

Typically, the amount of magnesium in OPC is carefully monitored. When aquarry encounters a seam of magnesium bearing rocks, which would causethem to exceed the magnesium limit, then the quarry may be forced tomanage that material separately. If the magnesium content is too high,then the quarry may be forced to set the material aside and not use itor to use it for a low value operation such as building roads in thequarry. Having to set quarried rock aside is undesirable because thequarry may still have the expense of blasting and transporting the rockbut may not have the value of the cement produced from the highmagnesium rock. However, the unique compositions, methods and systemscomprising the vaterite and the magnesium oxide provided herein, add anadditional advantage of utilizing these high magnesium bearing rocks byproducing the cementitious composition comprising the vaterite and themagnesium oxide. The magnesium oxide in the compositions may be inreactive form that converts to the magnesium hydroxide upon hydration(cementation process).

In some embodiments, the composition comprising the vaterite and themagnesium oxide possesses unique properties, including, but not limitedto, cementing properties by transforming to the aragonite and/or thecalcite and the magnesium hydroxide, respectively, which sets andcements with high compressive strength, durability, and hardness. Insome embodiments, the vaterite transformation to the aragonite and/orthe calcite results in the cement that can be used to form buildingmaterials and/or cementitious products such as, but not limited to,formed building materials such as construction panels, aggregate,concrete, etc. further described herein. In some embodiments, thevaterite may be used as a filler or supplementary cementitious material(SCM) when mixed with other cement such as Ordinary Portland Cement(OPC). The composition comprising the vaterite and the magnesium oxidemay be used as an aggregate where the vaterite and the magnesium oxideafter contact with the water transforms to the aragonite and/or thecalcite and the magnesium hydroxide, respectively, which sets andcements and which is then chopped up after cementation to form theaggregate. In some embodiments, the composition comprising the vateriteand the magnesium oxide after transformation to the aragonite and/orcalcite and the magnesium hydroxide, respectively, may be used as afiller in non-cementitious products such as paper product, polymerproduct, lubricant, adhesive, rubber product, chalk, asphalt product,paint, abrasive for paint removal, personal care product, cosmetic,cleaning product, personal hygiene product, ingestible product,agricultural product, soil amendment product, pesticide, environmentalremediation product, and combination thereof. Such non-cementitiousproducts have been described in U.S. Pat. No. 7,829,053, issued Nov. 9,2010, which is incorporated herein by reference in its entirety.

The compositions, methods and systems provided herein have severaladvantages, such as but not limited to, reduction of the carbon dioxideemissions through the incorporation of the carbon dioxide back into theprocess to form the composition comprising the vaterite and themagnesium oxide. Production of the vaterite containing composition, inthe methods and systems provided herein, offers advantages including,operating expense savings through the reduction in fuel consumption, andreductions in carbon footprint. Cement is a significant contributor toglobal carbon dioxide emissions with over 1.5 billion metric tonsemitted per year, corresponding to about 5% of total emissions. Over 50%of the cement emissions may result from the release of carbon dioxidefrom the decomposition of the limestone feedstock (CaCO₃→CaO+CO₂). Inthe methods and systems provided herein, the emissions of the CO₂ fromthe calcination of the limestone to the lime may be avoided byrecapturing it back in the cementitious vaterite and magnesium oxidematerial. By recapturing the carbon dioxide, the vaterite and themagnesium oxide composition has the potential to eliminate a significantamount of the cement carbon dioxide emissions and total global emissionsfrom all sources. The vaterite and magnesium oxide compositions providedherein can be used to replace the OPC either entirely in buildingapplications such as but not limited to, cement fiber board or partiallyas the SCM.

I. Methods and Systems

In one aspect, there are provided methods and systems to form thecomposition comprising the vaterite and the magnesium oxide.

In one aspect, there are provided methods to form the composition,comprising dissolving the lime and the magnesium oxide in the aqueousN-containing salt solution under one or more precipitation conditions toproduce the composition comprising vaterite and magnesium oxide.

In one aspect, there are provided methods to form the composition,comprising dissolving a mixture comprising lime and magnesium oxide inthe N-containing salt solution under one or more dissolution conditionsto produce the aqueous solution comprising calcium salt and magnesiumoxide; and treating the aqueous solution comprising calcium salt andmagnesium oxide with a gaseous stream comprising carbon dioxide underone or more precipitation conditions to form the composition comprisingvaterite and magnesium oxide.

In one aspect, there are provided methods to form the composition,comprising:

(i) calcining limestone to form a mixture comprising lime and magnesiumoxide, and a gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in theN-containing salt solution to produce the aqueous solution comprisingcalcium salt and magnesium oxide; and

(iii) treating the aqueous solution comprising calcium salt andmagnesium oxide with the gaseous stream comprising carbon dioxide toform the composition comprising vaterite and magnesium oxide.

In the aforementioned aspect, in some embodiments, the aqueous solutioncomprising calcium salt and magnesium oxide further comprises dissolvedammonia and/or dissolved N-containing salt.

In one aspect, there are provided methods to form the composition,comprising:

(i) calcining limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in theN-containing salt solution to produce the aqueous solution comprisingcalcium salt and magnesium oxide, and a gaseous stream comprisingammonia; and

(iii) treating the aqueous solution comprising calcium salt andmagnesium oxide with the gaseous stream comprising carbon dioxide andthe gaseous stream comprising ammonia to form the composition comprisingvaterite and magnesium oxide.

In one aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the aqueoussolution comprising calcium salt and magnesium oxide; and

(iii) a treatment reactor operably connected to the dissolution reactorand the calcination reactor configured for treating the aqueous solutioncomprising calcium salt and magnesium oxide with the gaseous streamcomprising carbon dioxide, to form the composition comprising vateriteand magnesium oxide.

In the aforementioned aspects, in some embodiments, the aqueous solutioncomprising calcium salt and magnesium oxide further comprises dissolvedammonia and/or dissolved N-containing salt.

In one aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the aqueoussolution comprising calcium salt and magnesium oxide, and a gaseousstream comprising ammonia; and

(iii) a treatment reactor operably connected to the dissolution reactorand the calcination reactor configured for treating the aqueous solutioncomprising calcium salt and magnesium oxide with the gaseous streamcomprising carbon dioxide and the gaseous stream comprising ammonia, toform the composition comprising vaterite and magnesium oxide.

In some embodiments of the aforementioned aspect, the aqueous solutionfurther comprises ammonia and/or the N-containing salt.

Some aspects and embodiments of the methods and systems provided hereinare as illustrated in FIGS. 1-4 . It is to be understood that the stepsillustrated in FIGS. 1-4 may be modified or the order of the steps maybe changed or more steps may be added or deleted depending on thedesired outcome. As illustrated in FIGS. 1-4 , the lime is subjected tomethods and systems provided herein to produce the compositioncomprising vaterite and magnesium oxide

The “lime” or “CaO” as used herein relates to calcium oxide and/orcalcium hydroxide. The presence and amount of the calcium oxide and/orthe calcium hydroxide in the lime would vary depending on the conditionsfor the lime formation.

The calcination or the calcining is a thermal treatment process to bringabout a thermal decomposition of the limestone. The “limestone” as usedherein, means CaCO₃ and may further include other minerals typicallypresent in the limestone. Limestone is a naturally occurring material.The chemical composition of this material may vary from region to regionas well as between different deposits in the same region. Therefore, thelime containing the calcium oxide and/or the calcium hydroxide obtainedfrom calcining the limestone from each natural deposit may be different.The limestone may be composed of calcium carbonate (CaCO₃), magnesiumcarbonate (MgCO₃), silica (SiO₂), alumina (Al₂O₃), iron (Fe), sulfur (S)or other trace elements.

The limestone deposits are widely distributed. The limestone from thevarious deposits may differ in physical chemical properties and can beclassified according to their chemical composition, texture andgeological formation. The limestone may be classified into the followingtypes: high calcium limestone where the carbonate content may becomposed mainly of calcium carbonate with a magnesium carbonate contentnot more than 5%; magnesium limestone containing magnesium carbonate toabout 5-35%; or dolomitic limestone which may contain between 35-46% ofMgCO₃, the balance amount is calcium carbonate. The limestone fromdifferent sources may differ considerably in chemical compositions andphysical structures. It is to be understood that the methods and systemsprovided herein apply to all the cement plants calcining the limestonefrom any of the sources listed above or commercially available. Thequarries include, but not limited to, quarries associated with cementkilns, quarries for lime rock for aggregate for use in concrete,quarries for lime rock for other purposes (road base), and/or quarriesassociated with lime kilns.

The limestone calcination is a decomposition process where the chemicalreaction for the decomposition of the limestone is:CaCO₃→CaO+CO₂(g)

The limestone may comprise one or more magnesium bearing mineral. Insome embodiments of the foregoing aspects, the limestone comprisesbetween about 1-70% magnesium or magnesium bearing mineral or betweenabout 1-60%, or between about 1-50%, or between about 1-40%, or betweenabout 1-30%, or between about 1-20%, or between about 1-10% magnesium ormagnesium bearing mineral.

In some embodiments, the limestone may be a pure calcium carbonate. Insome embodiments, the limestone may comprise the magnesium or themagnesium bearing mineral and/or a separate magnesium bearing mineralmay be mixed with the limestone before and/or during the calcination.The “magnesium bearing mineral” as used herein includes any mineral thatcontains the magnesium.

In some embodiments of the foregoing aspects and embodiments, themagnesium in the limestone and/or the magnesium bearing mineral upon thecalcination partially or fully forms the magnesium oxide. The chemicalequation of the formation of the magnesium oxide from the magnesiumbearing mineral, e.g., magnesium carbonate is as below:MgCO₃→MgO+CO₂(g)

In some embodiments of the foregoing aspects and embodiments, themagnesium bearing mineral comprises magnesium carbonate, such as, e.g.,calcium magnesium carbonate, magnesium salt, such as, e.g., potassiummagnesium salt, magnesium hydroxide, magnesium silicate, such as, e.g.,magnesium iron silicate, magnesium sulfate, or combination thereof. Insome embodiments of the foregoing aspects and embodiments, the magnesiumbearing mineral is selected from the group consisting of dolomite(CaMg(CO₃)₂), magnesite, brucite (Mg(OH₂), carnallite (KMgCl₃·6(H₂O)),talc (Mg₃Si₄O₁₀(OH)₂), olivine ((Mg²⁺, Fe²⁺)₂SiO₄), and combinationthereof. Other examples include, without limitation, artinite(MgCO₃·Mg(OH)₂·3H₂O), hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O), dypingite(4MgCO₃·Mg(OH)₂·5H₂O), barringonite (MgCO₃·2H₂O), nesquehonite(MgCO₃·3H₂O), iansfordite (MgCO₃·5H₂O), kieserite (MgSO₄·H₂O) or anyother hydration state of magnesium carbonate or sulfate. Sometimes themagnesium bearing mineral occurs with the limestone.

This step is illustrated in FIGS. 1-3 as a first step of the calcinationof the limestone comprising the magnesium bearing mineral and/orcombined with the magnesium bearing mineral to form the mixturecomprising lime and magnesium oxide. The lime may be in dry form i.e.,calcium oxide, and/or in wet form e.g., calcium hydroxide, depending onthe conditions. The production of the lime may depend upon the type ofkiln, conditions of the calcination, and the nature of the raw materiali.e., the limestone. At relatively low calcination temperatures,products formed in the kiln may contain both un-burnt carbonate and limeand may be called under burnt lime. As the temperature increases, softburnt or high reactive lime may be produced. At still highertemperatures, dead burnt or low reactive lime may be produced. Softburnt lime is produced when the reaction front reaches the core of thecharged limestone and converts all carbonate present to the lime. A highproductive product may be relatively soft, contains small limecrystallites and/or has open porous structure with an easily assessableinterior. Such lime may have the optimum properties of high reactivity,high surface area and low bulk density. Increasing the degree ofcalcination beyond this stage may make lime crystallites grow larger,agglomerate and sinter. This may result in a decrease in surface area,porosity and reactivity and an increase in bulk density. This productmay be known as dead burnt or low reactive lime. Without being limitedby any theory, the methods and systems provided herein utilize any oneor the combination of the aforementioned lime. Therefore, in someembodiments, the lime is under burnt lime, soft burnt lime, dead burntlime, or combination thereof. Similarly, at relatively low calcinationtemperatures, products formed in the kiln may contain both un-burntmagnesium bearing mineral and the magnesium oxide and may be calledunder burnt magnesium oxide. As the temperature increases, soft burnt orhigh reactive magnesium oxide may be produced. At still highertemperatures, dead burnt or low reactive magnesium oxide may beproduced. Soft burnt magnesium oxide is produced when the reaction frontreaches the core of the charged magnesium bearing mineral and convertsthe magnesium bearing mineral present to magnesium oxide. A highproductive product may be relatively soft, contains small magnesiumoxide crystallites. Such magnesium oxide may have the optimum propertiesof high reactivity, high surface area and low bulk density. Increasingthe degree of the calcination beyond this stage may make magnesium oxidecrystallites to grow larger, agglomerate and sinter. This may result ina decrease in surface area, porosity and reactivity and an increase inbulk density. This product may be known as dead burnt or low reactivemagnesium oxide. In some embodiments, the aforementioned reactivity ofthe magnesium oxide relates to its ability to bind with water to formmagnesium hydroxide (Mg(OH)₂).

In some embodiments, the calcination temperature to calcine thelimestone and/or the magnesium bearing mineral is between about 300°C.-1200° C.; or between about 400° C.-1200° C.; or between about 500°C.-1200° C.; or between about 600° C.-1200° C.; or between about 700°C.-1200° C.; or between about 800° C.-1200° C.; or between about 900°C.-1200° C.; or between about 1000° C.-1200° C.; or between about 300°C.-1200° C.; or between about 300° C.-1000° C.; or between about 300°C.-800° C.; or between about 300° C.-500° C.

In some embodiments, the methods and systems provided herein furthercomprise controlling the calcination process to control components ofthe mixture comprising the lime and the magnesium oxide. In someembodiments, the calcination process may be controlled in order toobtain the soft burnt or reactive lime as well as the soft burntmagnesium oxide. In some embodiments, the calcination process may becontrolled by controlling the temperature and/or duration of the heatingof the limestone. In some embodiments, the methods and systems providedherein further comprise controlling the calcination temperature betweenabout 300° C.-1200° C.; or between about 300° C.-800° C., to burn orfire the lime and the magnesium bearing mineral.

Production of the lime by calcining the limestone may be carried outusing various types of kilns, such as, but not limited to, a shaft kilnor a rotary kiln or an electric kiln. The use of the electric kiln inthe calcination and the advantages associated with it, have beendescribed in U.S. Provisional Application No. 63/046,239, filed Jun. 30,2020, which is fully incorporated herein by reference in its entirety.

These apparatuses for the calcining or the calcination reactors aresuitable for calcining the limestone in the form of lumps havingdiameters of several to tens of millimeters. Cement plant waste streamsinclude waste streams from both wet process and dry process plants,which plants may employ shaft kilns, rotary kilns, electric kilns, orcombinations thereof and may include pre-calciners. These industrialplants may each burn a single fuel or may burn two or more fuelssequentially or simultaneously.

As illustrated in FIGS. 1-3 , the limestone comprising the magnesiumbearing mineral and/or combined with the magnesium bearing mineral issubjected to the calcination in the cement plant resulting in theformation of the mixture comprising the lime and the magnesium oxide,and the CO₂ gas. The lime may be the calcium oxide in the form of asolid from dry kilns/cement processes and/or may be a combination of thecalcium oxide and the calcium hydroxide in the form of slurry in wetkilns/cement processes. When wet the calcium oxide (also known as a baseanhydride that converts to its hydroxide form in water) may be presentin its hydrated form such as but not limited to, the calcium hydroxide.While the calcium hydroxide (also called slaked lime) is a commonhydrated form of the calcium oxide, other intermediate hydrated and/orwater complexes may also be present in the slurry and are all includedwithin the scope of the methods and systems provided herein. It is to beunderstood that while the lime is illustrated as CaO in some of thefigures herein, it may be present as Ca(OH)₂ or combination of CaO andCa(OH)₂.

The lime may be sparingly soluble in water. In the methods and systemsprovided herein, the lime solubility is increased by its treatment withsolubilizers.

In the methods and systems provided herein, the mixture comprising limeand magnesium oxide is solvated or dissolved or solubilized with asolubilizer in a dissolution reactor, such as an aqueous weak acidsolution, such as N-containing salt solution (step A in FIGS. 1-3 )under one or more dissolution conditions to produce the aqueous solutioncomprising calcium salt and magnesium oxide. For illustration purposesonly, the N-containing salt, e.g., N-containing inorganic salt solutionis being illustrated in the figures as ammonium chloride (NH₄Cl)solution and the subsequent calcium salt is being illustrated as calciumchloride (CaCl₂). Various examples of the N-containing salt have beenprovided herein and are all within the scope of the invention.

The N-containing salt include without limitation, N-containing inorganicsalt, N-containing organic salt, or combination thereof.

The “N-containing inorganic salt” as used herein includes any inorganicsalt with nitrogen in it. Examples of N-containing inorganic saltinclude, but not limited to, ammonium halide (halide is any halogen),ammonium acetate, ammonium sulfate, ammonium sulfite, ammonium nitrate,ammonium nitrite, and the like. In some embodiments, the ammonium halideis ammonium chloride or ammonium bromide. In some embodiments, theammonium halide is ammonium chloride.

The “N-containing organic salt” as used herein includes any salt of anorganic compound with nitrogen in it. Examples of N-containing organiccompounds include, but not limited to, aliphatic amine, alicyclic amine,heterocyclic amine, and combinations thereof.

The “aliphatic amine” as used herein includes any alkyl amine of formula(R)_(n)—NH_(3-n) where n is an integer from 1-3, wherein R isindependently between C1-C8 linear or branched and substituted orunsubstituted alkyl. An example of the corresponding halide salt(chloride salt, bromide salt, fluoride salt, or iodide salt) of thealkyl amine of formula (R)_(n)—NH_(3-n) is (R)_(n)—NH_(4-n) ⁺Cl⁻. Insome embodiments, when R is substituted alkyl, the substituted alkyl isindependently substituted with halogen, hydroxyl, acid and/or ester.

For example, when R is alkyl in (R)_(n)—NH_(3-n), the alkyl amine can bea primary alkyl amine, such as for example only, methylamine,ethylamine, butylamine, pentylamine, etc.; the alkyl amine can be asecondary amine, such as for example only, dimethylamine, diethylamine,methylethylamine, etc.; and/or the alkyl amine can be a tertiary amine,such as for example only, trimethylamine, triethylamine, etc.

For example, when R is substituted alkyl substituted with hydroxyl in(R)_(n)—NH_(3-n), the substituted alkyl amine is an alkanolamineincluding, but not limited to, monoalkanolamine, dialkanolamine, ortrialkanolamine, such as e.g., monoethanolamine, diethanolamine, ortriethanolamine, etc.

For example, when R is substituted alkyl substituted with halogen in(R)_(n)—NH_(3-n), the substituted alkyl amine is, for example,chloromethylamine, bromomethylamine, chloroethylamine, bromoethylamine,etc.

For example, when R is substituted alkyl substituted with acid in(R)_(n)—NH_(3-n), the substituted alkyl amine is, for example, aminoacids. In some embodiments, the aforementioned amino acid has a polaruncharged alkyl chain, examples include without limitation, serine,threonine, asparagine, glutamine, or combinations thereof. In someembodiments, the aforementioned amino acid has a charged alkyl chain,examples include without limitation, arginine, histidine, lysine,aspartic acid, glutamic acid, or combinations thereof. In someembodiments, the aforementioned amino acid is glycine, proline, orcombination thereof.

The “alicyclic amine” as used herein includes any alicyclic amine offormula (R)_(n)—NH_(3-n) where n is an integer from 1-3, wherein R isindependently one or more all-carbon rings which may be either saturatedor unsaturated, but do not have aromatic character. Alicyclic compoundsmay have one or more aliphatic side chains attached. An example of thecorresponding salt of the alicyclic amine of formula (R)_(n)—NH_(3-n) is(R)_(n)—NH_(4-n) ⁺Cl⁻. Examples of alicyclic amine include, withoutlimitation, cycloalkylamine: cyclopropylamine, cyclobutylamine,cyclopentylamine, cyclohexylamine, cycloheptylamine, cyclooctylamine,and so on.

The “heterocyclic amine” as used herein includes at least oneheterocyclic aromatic ring attached to at least one amine. Examples ofheterocyclic rings include, without limitation, pyrrole, pyrrolidine,pyridine, pyrimidine, etc. Such chemicals are well known in the art andare commercially available.

In the methods and systems provided herein, the mixture comprising limeand magnesium oxide is dissolved or solubilized with the solubilizer,such as the N-containing salt solution (step A in FIGS. 1-3 ) under oneor more dissolution conditions to produce the aqueous solutioncomprising the calcium salt and the magnesium oxide. During and/or afterthe dissolution process, ammonia and/or the N-containing salt may remaindissolved in the aqueous solution and/or the gaseous stream comprisingammonia may be formed.

As illustrated in step A of FIGS. 1-3 , the N-containing salt isexemplified as ammonium chloride (NH₄Cl). The lime is solubilized bytreatment with NH₄Cl (new and recycled as further explained below) whenthe reaction that may occur is:CaO+2NH₄Cl(aq)→CaCl₂(aq)+2NH₃+H₂OCa(OH)₂+2NH₄Cl(aq)→2NH₃+CaCl₂+2H₂O

Similarly, when the base is N-containing organic salt, the reaction maybe shown as below:CaO+2NH₃RCl→CaCl₂(aq)+2NH₂R+H₂O

In some embodiments, the N-containing salt, such as, the N-containinginorganic salt such as, but not limited to, an ammonium salt, e.g., theammonium chloride solution or the ammonium acetate solution may besupplemented with anhydrous ammonia or an aqueous solution of ammonia tomaintain an optimum level of the N-containing salt, such as, theammonium chloride or the ammonium acetate in the solution.

In some embodiments, the aqueous solution comprising calcium salt andmagnesium oxide obtained after dissolution of the mixture comprisinglime and magnesium oxide may contain sulfur depending on the source ofthe lime. The sulfur may get introduced into the aqueous solution afterthe solubilization of the lime with any of the N-containing saltsdescribed herein. In an alkaline solution, various sulfur compoundscontaining various sulfur ionic species may be present in the solutionincluding, but not limited to, sulfite (SO₃ ²⁻), sulfate (SO₄ ²⁻),hydrosulfide (HS⁻), thiosulfate (S₂O₃ ²⁻), polysulfides (S_(n) ²⁻),thiol (RSH), and the like. The “sulfur compound” as used herein,includes any sulfur ion containing compound.

In some embodiments, the aqueous solution further comprises theN-containing salt, such as, ammonia and/or N-containing inorganic orN-containing organic salt.

In some embodiments, the amount of the N-containing salt such as, theN-containing inorganic salt, the N-containing organic salt, orcombinations thereof, is in more than 20% excess or more than 30% excessto the mixture comprising lime and magnesium oxide. In some embodiments,the molar ratio of the N-containing salt:the mixture comprising lime andmagnesium oxide (or the N-containing inorganic salt:the mixturecomprising lime and magnesium oxide; or the N-containing organicsalt:the mixture comprising lime and magnesium oxide; or the ammoniumchloride:the mixture comprising lime and magnesium oxide; or theammonium acetate:the mixture comprising lime and magnesium oxide) isbetween 0.5:1-3:1; or 0.5:1-2:1; or 0.5:1-1.5:1; or 1:1-1.5:1; or 1.5:1;or 2:1; or 2.5:1; or 1:1; or 3:1.

In some embodiments of the methods described herein, no polyhydroxycompounds are used to form the precipitation material and/or theproducts provided herein.

In some embodiments of the methods and systems described herein, the oneor more dissolution conditions are selected from the group consisting oftemperature between about 30-200° C., or between about 30-150° C., orbetween about 30-100° C., or between about 30-75° C., or between about30-50° C., or between about 40-200° C., or between about 40-150° C., orbetween about 40-100° C., or between about 40-75° C., or between about40-50° C., or between about 50-200° C., or between about 50-150° C., orbetween about 50-100° C.; pressure between about 0.1-50 atm, or betweenabout 0.1-40 atm, or between about 0.1-30 atm, or between about 0.1-20atm, or between about 0.1-10 atm, or between about 0.5-20 atm; theN-containing inorganic or organic salt wt % in water between about0.5-50%, or between about 0.5-25%, or between about 0.5-10%, or betweenabout 3-30%, or between about 5-20%; or combination thereof.

Agitation may be used to affect dissolution of the mixture comprisinglime and magnesium oxide with the aqueous N-containing salt solution inthe dissolution reactor, for example, by eliminating hot and cold spots.In some embodiments, the concentration of the lime and the magnesiumoxide in water may be between 1 and 10 g/L, 10 and 20 g/L, 20 and 30g/L, 30 and 40 g/L, 40 and 80 g/L, 80 and 160 g/L, 160 and 320 g/L, 320and 640 g/L, or 640 and 1280 g/L. To optimize the dissolution/solvationof the lime, high shear mixing, wet milling, and/or sonication may beused to break open the lime. During or after high shear mixing and/orwet milling, the lime suspension may be treated with the N-containingsalt solution.

In some embodiments, the dissolution of the mixture comprising lime andmagnesium oxide with the N-containing salt solution (illustrated ase.g., ammonium chloride) results in the formation of the aqueoussolution comprising calcium salt and solids. In some embodiments, themagnesium oxide formed after the calcination may stay as the solid andmay not dissolve or may dissolve partially in the N-containing saltsolution. This solid may and/or may not be separated from the aqueoussolution comprising calcium salt.

Accordingly, in one aspect, there are provided methods to form thecomposition, comprising:

(i) calcining limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in theN-containing salt solution to produce the aqueous solution comprisingcalcium salt and the solid comprising magnesium oxide;

(iii) separating the solid from the aqueous solution;

(iv) treating the aqueous solution comprising calcium salt with thegaseous stream comprising carbon dioxide to form the compositioncomprising vaterite; and

(v) mixing the composition comprising vaterite and the solid comprisingmagnesium oxide.

In one aspect, there are provided methods to form the composition,comprising:

(i) calcining limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in theN-containing salt solution to produce the aqueous solution comprisingcalcium salt, the solid comprising magnesium oxide, and the gaseousstream comprising ammonia;

(iii) separating the solid from the aqueous solution;

(iv) treating the aqueous solution comprising calcium salt with thegaseous stream comprising carbon dioxide and the gaseous streamcomprising ammonia to form the composition comprising vaterite; and

(v) mixing the composition comprising vaterite and the solid comprisingmagnesium oxide.

In one aspect, there are also provided methods to form the composition,comprising:

(i) calcining limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in theN-containing salt solution to produce the aqueous solution comprisingcalcium salt and the solid comprising magnesium oxide; and

(iii) treating the aqueous solution comprising calcium salt and thesolid comprising magnesium oxide with the gaseous stream comprisingcarbon dioxide to form the composition comprising vaterite and the solidcomprising magnesium oxide.

In one aspect, there are also provided methods to form the composition,comprising:

(i) calcining limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in theN-containing salt solution to produce the aqueous solution comprisingcalcium salt, the solid comprising magnesium oxide, and the gaseousstream comprising ammonia; and

(iii) treating the aqueous solution comprising calcium salt and thesolid comprising magnesium oxide with the gaseous stream comprisingcarbon dioxide and the gaseous stream comprising ammonia to form thecomposition comprising vaterite and the solid comprising magnesiumoxide.

In another aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the aqueoussolution comprising calcium salt and the solid comprising magnesiumoxide; and

(iii) a treatment reactor operably connected to the dissolution reactorand the calcination reactor configured for treating the aqueous solutioncomprising calcium salt and the solid comprising magnesium oxide withthe gaseous stream comprising carbon dioxide, to form the compositioncomprising vaterite and magnesium oxide.

In another aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the aqueoussolution comprising calcium salt, the solid comprising magnesium oxide,and the gaseous stream comprising ammonia; and

(iii) a treatment reactor operably connected to the dissolution reactorand the calcination reactor configured for treating the aqueous solutioncomprising calcium salt and the solid comprising magnesium oxide withthe gaseous stream comprising carbon dioxide and the gaseous streamcomprising ammonia, to form the composition comprising vaterite andmagnesium oxide.

In another aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the aqueoussolution comprising calcium salt and the solid comprising magnesiumoxide;

(iii) a separator operably connected to the dissolution reactorconfigured to separate the solid from the aqueous solution;

(iv) a treatment reactor operably connected to the separator, thedissolution reactor, and the calcination reactor configured for treatingthe aqueous solution comprising calcium salt with the gaseous streamcomprising carbon dioxide, to form the composition comprising vaterite;and

(v) a mixer operably connected to the treatment reactor and theseparator configured to mix the composition comprising vaterite and thesolid comprising magnesium oxide.

As noted in the aforementioned aspects, the solid comprising magnesiumoxide may and/or may not be separated from the aqueous solutioncomprising calcium salt, in the methods and systems provided herein.This step is illustrated as step B (including dashed arrows) in theFIGS. 1-3 .

In some embodiments, the solid comprising magnesium oxide may be removedfrom the aqueous solution of the calcium salt (shown as dashed linesfrom step B in FIGS. 1-3 ) before the aqueous solution is treated withthe carbon dioxide in the process. The solid comprising magnesium oxidemay optionally be removed or separated from the aqueous solution byseparators, such as e.g., filtration and/or centrifugation.

It is to be understood that the separation in step B in FIGS. 1-3 isoptional and in some embodiments, the solid comprising magnesium oxidemay not be removed from the aqueous solution and the aqueous solutioncomprising calcium salts as well as the solid comprising magnesium oxideare contacted with the carbon dioxide (in step C in FIGS. 1-3 ) to formthe precipitate. In such embodiments, the composition comprisingvaterite further comprises solid comprising magnesium oxide.

In some embodiments, the solid comprising magnesium oxide obtained afterthe dissolution of the lime further comprises calcium depleted solid andmay optionally be used as a cement substitute (such as a substitute forPortland cement). In some embodiments, the solid comprising magnesiumoxide, may further comprise silicate, iron oxide, aluminate, orcombination thereof. The silicate includes, without limitation, clay(phyllosilicate), alumino-silicate, etc.

In some embodiments, the solid comprising magnesium oxide is between1-75 wt %; or between 1-70 wt %; or between 1-60 wt %; or between 1-50wt %; or between 1-40 wt %; or between 1-30 wt %; or between 1-20 wt %;or between 1-10 wt % or between 1-5 wt %; or between 1-2 wt %, in theaqueous solution, in the vaterite cake, in the composition comprisingvaterite, or combination thereof. In some embodiments, the solidcomprising magnesium oxide is between 1-75 wt %; or between 1-70 wt %;or between 1-60 wt %; or between 1-50 wt %; or between 1-40 wt %; orbetween 1-30 wt %; or between 1-20 wt %; or between 1-10 wt % or between1-5 wt %; or between 1-2 wt %, of dissolved cement mass. In someembodiments, the solid comprising magnesium oxide is between 1-75 wt %;or between 1-70 wt %; or between 1-60 wt %; or between 1-50 wt %; orbetween 1-40 wt %; or between 1-30 wt %; or between 1-20 wt %; orbetween 1-10 wt % or between 1-5 wt %; or between 1-2 wt % of totalsolid produced (vaterite and solid).

As illustrated in step C in FIG. 1 , the aqueous solution comprisingcalcium salt and magnesium oxide and optionally the solid comprisingmagnesium oxide and dissolved ammonia and/or ammonium salt is contactedunder one or more precipitation conditions with the gaseous streamcomprising carbon dioxide recycled from the calcination step of therespective process, to form the composition/precipitation materialcomprising vaterite, magnesium oxide, and a supernatant solution, shownin the reaction below:CaCl₂(aq)+2NH₃(aq)+MgO+CO₂(g)+H₂O→CaCO₃(s)+MgO+2NH₄Cl(aq)

The absorption of the CO₂ into the aqueous solution produces CO₂-chargedwater containing carbonic acid, a species in equilibrium with bothbicarbonate and carbonate. The precipitation material/composition isprepared under the one or more precipitation conditions (as describedherein) suitable to form the vaterite.

In some embodiments, as illustrated in FIG. 2 , the gaseous streamcomprising CO₂ from the calcination step and the gaseous streamcomprising NH₃ from step A of the process is recirculated to theprecipitation reactor (step C) for the formation of thecomposition/precipitation material. Remaining steps of FIG. 2 areidentical to the steps of FIG. 1 . It is to be understood that theprocesses of both FIG. 1 and FIG. 2 can also take place simultaneouslysuch that the N-containing salt, such as the N-containing inorganic saltor the N-containing organic salt and the by-product ammonia may bepartially present in the aqueous solution and partially present in thegaseous stream.

The reaction taking place in the aforementioned aspect may be shown asbelow:CaCl₂(aq)+2NH₃(g)+CO₂(g)+MgO+H₂O→CaCO₃(s)+MgO+2NH₄Cl(aq)

In some embodiments of the aspects and embodiments provided herein, thegaseous stream comprising ammonia may have ammonia from an externalsource and/or is recovered and recirculated from step A of the process.

In some embodiments of the aspects and embodiments provided herein,wherein the gaseous stream comprises ammonia and/or the gaseous streamcomprises carbon dioxide, no external source of carbon dioxide and/orammonia is used, and the process is a closed loop process. Such closedloop process is being illustrated in the figures described herein.

In some embodiments, the dissolution of the mixture comprising lime andmagnesium oxide with the N-containing organic salt may not result in theformation of the ammonia gas or the amount of ammonia gas formed may notbe substantial. In embodiments where the ammonia gas is not formed or isnot formed in substantial amounts, the methods and systems illustratedin FIG. 1 where the aqueous solution comprising calcium salt is treatedwith the carbon dioxide gas, are applicable. In such embodiments, theorganic amine salt may remain in the aqueous solution in fully orpartially dissolved state or may separate as an organic amine layer, asshown in the reaction below:CaO+MgO+2NH₃R⁺Cl⁻→CaCl₂(aq)+MgO+2NH₂R+H₂O

The N-containing organic salt or the N-containing organic compoundremaining in the supernatant solution after the precipitation may becalled residual N-containing organic salt or residual N-containingorganic compound. Methods and systems have been described herein torecover the residual compounds from the precipitate as well as thesupernatant solution.

In one aspect, there are provided methods to form the composition,comprising:

(i) calcining the limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide, in theaqueous N-containing salt solution to produce a first aqueous solutioncomprising calcium salt and magnesium oxide, and the gaseous streamcomprising ammonia;

(iii) recovering the gaseous stream comprising carbon dioxide and thegaseous stream comprising ammonia and subjecting the gaseous streams toa cooling process to condense a second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, ammonia carbamate, orcombinations thereof; and

(iv) treating the first aqueous solution comprising calcium salt andmagnesium oxide with the second aqueous solution comprising ammoniumbicarbonate, ammonium carbonate, ammonia, ammonia carbamate, orcombinations thereof to form the composition comprising vaterite andmagnesium oxide.

In one aspect, there are provided methods to form the composition,comprising:

(i) calcining the limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide, in theaqueous N-containing salt solution to produce the first aqueous solutioncomprising calcium salt, the solid comprising magnesium oxide, and thegaseous stream comprising ammonia;

(iii) separating the solid from the first aqueous solution;

(iv) recovering the gaseous stream comprising carbon dioxide and thegaseous stream comprising ammonia and subjecting the gaseous streams tothe cooling process to condense the second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, ammonia carbamate, orcombinations thereof;

(v) treating the first aqueous solution comprising calcium salt with thesecond aqueous solution comprising ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonia carbamate, or combinations thereof to formthe composition comprising vaterite; and

(vi) mixing the composition comprising vaterite and the solid comprisingmagnesium oxide.

In one aspect, there are provided methods to form the composition,comprising:

(i) calcining the limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide, in theaqueous N-containing salt solution to produce the first aqueous solutioncomprising calcium salt, the solid comprising magnesium oxide, and thegaseous stream comprising ammonia;

(iii) recovering the gaseous stream comprising carbon dioxide and thegaseous stream comprising ammonia and subjecting the gaseous streams tothe cooling process to condense the second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, ammonia carbamate, orcombinations thereof; and

(iv) treating the first aqueous solution comprising calcium salt and thesolid comprising magnesium oxide with the second aqueous solutioncomprising ammonium bicarbonate, ammonium carbonate, ammonia, ammoniacarbamate, or combinations thereof to form the composition comprisingvaterite and the solid comprising magnesium oxide.

In one aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine the limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the firstaqueous solution comprising calcium salt and magnesium oxide, and thegaseous stream comprising ammonia;

(iii) a cooling reactor operably connected to the dissolution reactorand the calcination reactor configured for recovering the gaseous streamcomprising carbon dioxide and the gaseous stream comprising ammonia andsubjecting the gaseous streams to the cooling process to condense thesecond aqueous solution comprising ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonium carbamate, or combinations thereof; and

(iv) a treatment reactor operably connected to the dissolution reactorand the cooling reactor configured for treating the first aqueoussolution comprising calcium salt and magnesium oxide with the secondaqueous solution comprising ammonium bicarbonate, ammonium carbonate,ammonia, ammonium carbamate, or combinations thereof to form thecomposition comprising vaterite and magnesium oxide.

In another aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine the limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the firstaqueous solution comprising calcium salt, the solid comprising magnesiumoxide, and the gaseous stream comprising ammonia;

(iii) a separator operably connected to the dissolution reactorconfigured to separate the solid from the first aqueous solution;

(iv) a cooling reactor operably connected to the dissolution reactor andthe calcination reactor configured for recovering the gaseous streamcomprising carbon dioxide and the gaseous stream comprising ammonia andsubjecting the gaseous streams to the cooling process to condense thesecond aqueous solution comprising ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonium carbamate, or combinations thereof;

(v) a treatment reactor operably connected to the separator and thecooling reactor configured for treating the first aqueous solution withthe second aqueous solution to form the composition comprising vaterite;and

(vi) a mixer operably connected to the treatment reactor and theseparator configured to mix the composition comprising vaterite and thesolid comprising magnesium oxide.

In another aspect, there are provided systems to form the composition,comprising:

(i) a calcining reactor configured to calcine the limestone to form themixture comprising lime and magnesium oxide, and the gaseous streamcomprising carbon dioxide;

(ii) a dissolution reactor operably connected to the calcination reactorconfigured for dissolving the mixture comprising lime and magnesiumoxide in the aqueous N-containing salt solution to produce the firstaqueous solution comprising calcium salt, the solid comprising magnesiumoxide, and the gaseous stream comprising ammonia;

(iii) a cooling reactor operably connected to the dissolution reactorand the calcination reactor configured for recovering the gaseous streamcomprising carbon dioxide and the gaseous stream comprising ammonia andsubjecting the gaseous streams to the cooling process to condense thesecond aqueous solution comprising ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonium carbamate, or combinations thereof; and

(iv) a treatment reactor operably connected to the dissolution and thecooling reactor configured for treating the first aqueous solution andthe solid comprising magnesium oxide with the second aqueous solution,to form the composition comprising vaterite and the solid comprisingmagnesium oxide.

The aforementioned aspects are illustrated in FIG. 3 , wherein thegaseous stream comprising CO₂ from the calcination step/reactor and thegaseous stream comprising NH₃ from step A of the process is recirculatedto the cooling reactor/reaction (step F) for the formation of thecarbonate and bicarbonate solutions as shown in the reactions furtherherein below. Remaining steps of FIG. 3 are identical to the steps ofFIGS. 1 and 2 . It is to be understood that the first aqueous solutioncomprising calcium salt as provided herein is same as the aqueoussolution comprising calcium salt described herein. The aqueous solutioncomprising calcium salt is described as first aqueous solution only forclarity when it needs to be differentiated from the second aqueoussolution.

It is to be understood that the aforementioned aspects illustrated inFIG. 3 may be combined with the aspects illustrated in FIG. 1 and/orFIG. 2 such that the precipitation step C comprises treating the firstaqueous solution comprising calcium salt and magnesium oxide or thesolid comprising magnesium oxide with the second aqueous solutioncomprising ammonium bicarbonate, ammonium carbonate, ammonia, orcombinations thereof (illustrated in FIG. 3 ), as well as comprisestreating the aqueous solution comprising calcium salt and magnesiumoxide or the solid comprising magnesium oxide with the gaseous streamcomprising carbon dioxide (illustrated in FIG. 1 ) and/or comprisestreating the aqueous solution comprising calcium salt and magnesiumoxide or the solid comprising magnesium oxide with the gaseous streamcomprising carbon dioxide and the gaseous stream comprising ammonia(illustrated in FIG. 2 ). In such embodiments, the gaseous streamcomprising carbon dioxide is split between the stream going to thecooling process and the stream going to the precipitation process.Similarly, in such embodiments, the gaseous stream comprising ammonia issplit between the stream going to the cooling process and the streamgoing to the precipitation process. Any combination of the processesdepicted in FIGS. 1-3 is possible and all are within the scope of thisdisclosure.

In some embodiments of the aforementioned aspects, the second aqueoussolution comprises ammonium carbamate. Ammonium carbamate has a formulaNH₄[H₂NCO₂] consisting of ammonium ions NH₄ ⁺, and carbamate ions H₂NCO₂⁻. In some embodiments of the aforementioned aspect and embodiments, thesecond aqueous solution comprises ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonium carbamate, or combinations thereof.

The combination of these condensed products in the second aqueoussolution may be dependent on the one or more of the cooling conditions.Table 1 presented below represents various combinations of the condensedproducts in the second aqueous solution.

TABLE 1 Order Rectangular pulse train amplitude vector 2 1 −1 3 1 −2 1 41 −3 3 −1 5 1 −4 6 −4 1 6 1 −5 10 −10 5 −1 7 1 −6 15 −20 15 −6 1 8 1 −721 −35 35 −21 7 −1 9 1 −8 28 −56 70 −56 28 −8 1 10 1 −9 36 −84 126 −12684 −36 9 −1

In some embodiments of the aforementioned aspect and embodiments, thegaseous stream (e.g., the gaseous streams going to the coolingreaction/reactor (step F in FIG. 3 )) further comprises water vapor. Insome embodiments of the aforementioned aspect and embodiments, thegaseous stream further comprises between about 20-90%; or between about20-80%; or between about 20-70%; or between about 20-60%; or betweenabout 20-55%; or between about 20-50%; or between about 20-40%; orbetween about 20-30%; or between about 20-25%; or between about 30-90%;or between about 30-80%; or between about 30-70%; or between about30-60%; or between about 30-50%; or between about 30-40%; or betweenabout 40-90%; or between about 40-80%; or between about 40-70%; orbetween about 40-60%; or between about 40-50%; or between about 50-90%;or between about 50-80%; or between about 50-70%; or between about50-60%; or between about 60-90%; or between about 60-80%; or betweenabout 60-70%; or between about 70-90%; or between about 70-80%; orbetween about 80-90%, water vapor.

In some embodiments of the aforementioned aspect and embodiments, noexternal water is added to the cooling process. It is to be understoodthat the cooling process is similar to condensation of the gases (butnot similar to the absorption of the gases) in the existing water vaporssuch that the gases are not absorbed in the water but are as such cooleddown together with the water vapors. Condensation of the gases into aliquid stream may provide process control advantages compared toabsorbing the vapors. For example only, the condensation of the gasesinto the liquid stream may allow pumping of the liquid stream into theprecipitation step. Pumping of the liquid stream may be lower in costthan compression of a vapor stream into the absorption process.

Intermediate steps in the cooling reaction/reactor may include theformation of ammonium carbonate and/or ammonium bicarbonate and/orammonium carbamate, by reactions as below:2NH₃+CO₂+H₂O→(NH₄)₂CO₃NH₃+CO₂+H₂O→(NH₄)HCO₃2NH₃+CO₂→(NH₄)NH₂CO₂

Similar reactions may be shown for the N-containing organic salt:2NH₂R+CO₂+H₂O→(NH₃R)₂CO₃NH₂R+CO₂+H₂O→(NH₃R)HCO₃

An advantage of cooling the ammonia in the cooling reaction/reactor isthat ammonia may have a limited vapor pressure in the vapor phase of thedissolution reaction. By reacting the ammonia with CO₂, as shown in thereactions above, can remove some ammonia from the vapor space, allowingmore ammonia to leave the dissolution solution.

The second aqueous solution comprising ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonium carbamate, or combinations thereof (exitingthe cooling reaction/reactor in FIG. 3 ) is then treated with the firstaqueous solution comprising calcium salt and magnesium oxide or thesolid comprising magnesium oxide from the dissolution reaction/reactor,in the precipitation reaction/reactor (step C) to form thecomposition/precipitation material comprising vaterite and magnesiumoxide:(NH₄)₂CO₃+CaCl₂+MgO→CaCO₃(vaterite)+MgO+2NH₄Cl(NH₄)HCO₃+NH₃+CaCl₂+MgO→CaCO₃(vaterite)+MgO+2NH₄Cl+H₂O2(NH₄)HCO₃+CaCl₂+MgO→CaCO₃(vaterite)+MgO+2NH₄Cl+H₂O+CO₂(NH₄)NH₂CO₂+H₂O+CaCl₂+MgO→CaCO₃(vaterite)+MgO+2NH₄Cl

Independent of any intermediate steps, the combination of the reactionslead to an overall process chemistry of:CaO(lime)+MgO→CaCO₃(vaterite)+MgO

In some embodiments of the aspects and embodiments provided herein, theone or more cooling conditions comprise temperature between about 0-200°C., or between about 0-150° C., or between about 0-75° C., or betweenabout 0-100° C., or between about 0-80° C., or between about 0-60° C.,or between about 0-50° C., or between about 0-40° C., or between about0-30° C., or between about 0-20° C., or between about 0-10° C., orbetween about 10-100° C., or between about 10-80° C., or between about10-60° C., or between about 10-50° C., or between about 10-40° C., orbetween about 10-30° C., or between about 20-100° C., or between about20-80° C., or between about 20-60° C., or between about 20-50° C., orbetween about 20-40° C., or between about 20-30° C., or between about30-100° C., or between about 30-80° C., or between about 30-60° C., orbetween about 30-50° C., or between about 30-40° C., or between about40-100° C., or between about 40-80° C., or between about 40-60° C., orbetween about 50-100° C., or between about 50-80° C., or between about60-100° C., or between about 60-80° C., or between about 70-100° C., orbetween about 70-80° C.

In some embodiments of the aspects and embodiments provided herein, theone or more cooling conditions comprise pressure between about 0.5-50atm; or between about 0.5-25 atm; or between about 0.5-10 atm; orbetween about 0.1-10 atm; or between about 0.5-1.5 atm; or between about0.3-3 atm.

In some embodiments, the formation and the quality of the compositioncomprising the vaterite and the magnesium oxide formed in the methodsand systems provided herein, is dependent on the amount and/or the ratioof the condensed products in the second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, ammonium carbamate,or combinations thereof.

In some embodiments, the presence or absence or distribution of thecondensed products in the second aqueous solution comprising ammoniumbicarbonate, ammonium carbonate, ammonia, ammonium carbamate, orcombinations thereof, can be controlled in order to maximize theformation of the composition comprising the vaterite and the magnesiumoxide and/or to obtain a desired particle size distribution. Thiscontrol can be based on the one or more cooling conditions, such as, pHof the aqueous solution in the cooling reactor, flow rate of the CO₂ andthe NH₃ gases, and/or ratio of the CO₂:NH₃ gases. The inlets for thecooling reactor (F in FIG. 3 ) may be carbon dioxide (CO_(2(g))), thedissolution reactor gas exhaust containing ammonia (NH_(3(g))), watervapor, and optionally fresh makeup water (or some other dilute waterstream). The outlet may be a slipstream of the reactor's recirculatingfluid (the second aqueous solution), which is directed to theprecipitation reactor for contacting with the first aqueous solution andoptionally additional carbon dioxide and/or ammonia. The pH of thesystem may be controlled by regulating the flow rate of the CO₂ and theNH₃ into the cooling reactor. The conductivity of the system may becontrolled by addition of dilute makeup water to the cooling reactor.Volume may be maintained constant by using a level detector in thecooling reactor or it's reservoir.

In some embodiments, higher pH of the aqueous solution in the coolingreactor (may be achieved by higher flow rate of ammonia) may favorcarbamate formation whereas lower pH of the aqueous solution in thecooling reactor (may be achieved by lower flow rate of ammonia) mayfavor carbonate and/or bicarbonate formation. In some embodiments, theone or more cooling conditions include pH of the aqueous solution formedin the cooling reactor to be between about 8-12, or between about 8-11,or between about 8-10, or between about 8-9.

In some embodiments, the flow rate of the carbon dioxide can be modifiedto achieve a desired pH of the second aqueous solution exiting thecooling reactor. For example, if the pH of the second aqueous solutionis high, the flow rate of the carbon dioxide can be increased to reducethe pH or if the pH of the second aqueous solution is low, the flow rateof the carbon dioxide can be reduced to increase the pH.

In some embodiments, the one or more cooling conditions include ratio ofCO₂:NH₃ in the cooling reactor to be between about 0.1:1-20:1, orbetween about 0.1:1-1:1, or between about 0.1:1-2:1, or between about5:1-10:1, or between about 1:1-5:1, or between about 2:1-5:1.

It is to be understood that while FIG. 3 illustrates a separate coolingreaction/reactor, in some embodiments, the dissolution reaction/reactormay be integrated with the cooling reaction/reactor, as illustrated inFIG. 4 . For example, the dissolution reactor may be integrated with acondenser acting as a cooling reactor. Both the mixture comprising thelime and the magnesium oxide and the aqueous N-containing salt solution(illustrated as NH₄Cl in FIG. 4 ) are fed to the dissolutionreaction/reactor, when the first aqueous solution comprising the calciumsalt (illustrated as CaCl₂) and the magnesium oxide is formed. Thesolution may optionally contain solid comprising the magnesium oxidethat may stay at the bottom of the dissolution reactor. The firstaqueous solution comprising the calcium salt (illustrated as CaCl₂) andthe magnesium oxide is withdrawn from the dissolution reaction/reactorto be processed further for precipitation. The gaseous stream comprisingammonia and water vapor passes to the upper section of the dissolutionreactor (i.e., the cooling reactor; illustrated in FIG. 4 ) where it iscooled along with the carbon dioxide to condense into the second aqueoussolution. The carbon dioxide may be obtained from a plant where thelimestone is being calcined into the lime and the carbon dioxide. Thecarbon dioxide is then fed to the vapor phase of the cooling reactor.The second aqueous solution comprising ammonium bicarbonate, ammoniumcarbonate, ammonia, ammonium carbamate, or combinations thereof, iscollected from the cooling reactor using various means, such as, e.g.,one or more trays (e.g., as illustrated in FIG. 4 ).

In one aspect, there is provided an integrated reactor comprising:

the dissolution reactor integrated with the cooling reactor wherein thedissolution reactor is positioned below the cooling reactor;

the dissolution reactor is configured to dissolve the mixture comprisinglime and magnesium oxide in the aqueous N-containing inorganic saltsolution or the N-containing organic salt solution to produce the firstaqueous solution comprising calcium salt and MgO, and the gaseous streamcomprising ammonia and water vapor; and

the cooling reactor operably connected to the dissolution reactor andconfigured to receive and condense the gaseous stream comprising ammoniaand water vapor from the dissolution reactor and the gaseous streamcomprising carbon dioxide from the calcination of the limestone to thelime; and form the second aqueous solution comprising ammoniumbicarbonate, ammonium carbonate, ammonia, ammonium carbamate, orcombinations thereof.

In some embodiments, the cooling reactor is packed with a packingmaterial. The packing material can be any inert material used to aidmass transfer of the NH₂ and the CO₂ from the vapor into the liquidphase. The packing can be random packing or structured packing. Therandom packing material can be any material that has individual piecespacked into the vessel or the reactor. The structured packing materialcan be any material that has an individual monolith that is shaped toprovide surface area and enhance mass transfer. Examples of loose orunstructured or random packing material include, but not limited to,Raschig rings (such as in ceramic material), pall rings (e.g., in metaland plastic), lessing rings, Michael Bialecki rings (e.g., in metal),berl saddles, intalox saddles (e.g., in ceramic), super intalox saddles,Tellerette® ring (e.g., spiral shape in polymeric material), etc.

Examples of structured packing material include, but not limited to,thin corrugated metal plates or gauzes (honeycomb structures) indifferent shapes with a specific surface area. The structured packingmaterial may be used as a ring or a layer or a stack of rings or layersthat have diameter that may fit into the diameter of the reactor. Thering may be an individual ring or a stack of rings fully filling thereactor. In some embodiments, the voids left out by the structuredpacking in the reactor are filled with the unstructured or randompacking material.

Examples of structured packing material includes, without limitation,Flexipac®, Intalox®, Flexipac® HC®, etc. In a structured packingmaterial, corrugated sheets may be arranged in a crisscross pattern tocreate flow channels for the vapor phase. The intersections of thecorrugated sheets may create mixing points for the liquid and vaporphases. The structured packing material may be rotated about the column(reactor) axis to provide cross mixing and spreading of the vapor andliquid streams in all directions. The structured packing material may beused in various corrugation sizes and the packing configuration may beoptimized to attain the highest efficiency, capacity, and pressure droprequirements of the reactor. The structured packing material may be madeof a material of construction including, but not limited to, titanium,stainless steel alloys, carbon steel, aluminum, nickel alloys, copperalloys, zirconium, thermoplastic, etc. The corrugation crimp in thestructured packing material may be of any size, including, but notlimited to, Y designated packing having an inclination angle of 45° fromthe horizontal or X designated packing having an inclination angle of60° from the horizontal. The X packing may provide a lower pressure dropper theoretical stage for the same surface area. The specific surfacearea of the structured packing may be between 50-800 m²/m³; or between75-350 m²/m³; or between 200-800 m²/m³; or between 150-800 m²/m³; orbetween 500-800 m²/m³.

In some embodiments, the cooling reactor further comprises an inlet tointroduce a scrubbing fluid, such as e.g., the ammonium chloridesolution or the ammonium acetate or the water to the top of the packingmaterial of the cooling reactor. The scrubbing fluids such as theammonium chloride solution, or the ammonium acetate solution or theammonia solution, or water or the like, facilitate formation of thecondensed products such as ammonium bicarbonate, ammonium carbonate,ammonia, ammonium carbamate, or combination thereof. The scrubbing fluidcan provide more liquid volume for the condensation of the gases. Insome embodiments, if the scrubbing fluid is pre-cooled, then it canfurther aid the condensation process. When the scrubbing fluid is theammonium chloride solution, the ammonium chloride solution can be aportion of the ammonium chloride solution being fed to the dissolutionreactor. In some embodiments, the second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, ammonium carbamate,ammonium chloride, or combination thereof, collected from the condensedliquid from the cooling reactor, may be recycled back to the coolingreactor as the scrubbing fluid to further facilitate the condensationprocess. In some embodiments, the second aqueous solution may be cooledin a heat exchanger prior to recycling it back to the cooling reactor.

Other gases such as flue gas in the gaseous stream comprising carbondioxide (obtained from the calcination process) may exit the coolingreactor (illustrated in FIG. 4 ).

In the aforementioned aspects, both the dissolution and the coolingreactors are fitted with inlets and outlets to receive the requiredgases and collect the aqueous streams. In some embodiments of theaforementioned aspects, the dissolution reactor comprises a stirrer tomix the mixture comprising the lime and the magnesium oxide with theaqueous N-containing salt solution. The stirrer can also facilitateupward movement of the gases. In some embodiments of the aforementionedaspects, the dissolution reactor is configured to collect the solidcomprising the magnesium oxide settled at the bottom of the reactorafter removing the first aqueous solution comprising the calcium saltand optionally the magnesium oxide. In some embodiments of theaforementioned aspect, the cooling tower comprises one or more traysconfigured to catch and collect the condensed second aqueous solutionand prevent it from falling back into the dissolution reactor. As such,the cooling/condensation may be accomplished through use of infusers,bubblers, fluidic Venturi reactors, spargers, gas filters, sprays,trays, or packed column reactors, and the like.

In some embodiments, the cooling reactor comprises a heat exchanger inthe reactor or a heat exchanging surface. The heat exchanger maycomprise one or more tubes with a cold fluid circulating inside thetubes such that the cold fluid is isolated from the vapor phase in thecooling reactor but facilitates lowering the temperature of the coolingreactor for the condensation of the gases. The cold fluid can be coolingwater, the scrubbing solution described above, and the like. In someembodiments, the second aqueous solution exiting the cooling reactor iscooled down by the heat exchanger before it is used as the scrubbingsolution.

As illustrated in step C in FIGS. 1-2 , the first aqueous solutioncomprising the calcium salt and the magnesium oxide, from the treatmentof the mixture comprising the lime and the magnesium oxide with theN-containing salt solution as described herein, such as e.g., theammonium salt e.g., the ammonium halide or the ammonium acetate, iscontacted with the CO₂ and optionally the NH₃ from step A at any timebefore, during, or after the aqueous solution comprising the calciumsalt and the magnesium oxide is subjected to the one or moreprecipitation conditions (i.e., conditions allowing for theprecipitation of the composition/precipitation material). Similarly, asillustrated in step C in FIG. 3 , the first aqueous solution comprisingthe calcium salt and the magnesium oxide, from the treatment of themixture comprising the lime and the magnesium oxide with theN-containing salt solution as described herein for step A, such as e.g.the ammonium salt e.g., the ammonium halide or the ammonium acetate, iscontacted with the second aqueous solution comprising ammoniumbicarbonate, ammonium carbonate, ammonia, ammonium carbamate, orcombinations thereof from the cooling reaction/reactor at any timebefore, during, or after the first aqueous solution comprising thecalcium salt and the magnesium oxide is subjected to the one or moreprecipitation conditions (i.e., conditions allowing for theprecipitation of the composition/precipitation material).

Accordingly, in some embodiments, the aqueous solution or the firstaqueous solution comprising the calcium salt and the magnesium oxide iscontacted with the CO₂ (and e.g., the NH₃ as in FIG. 2 or the secondaqueous solution as in FIG. 3 ) prior to subjecting the aqueous solutionor the first aqueous solution to the one or more precipitationconditions that favor formation of the composition comprising thevaterite and the magnesium oxide. In some embodiments, the aqueoussolution or the first aqueous solution comprising the calcium salt andthe magnesium oxide is contacted with the CO₂ (and e.g., the NH₃ as inFIG. 2 or the second aqueous solution as in FIG. 3 ) while the aqueoussolution or the first aqueous solution is being subjected to the one ormore precipitation conditions that favor formation of the compositioncomprising the vaterite and the magnesium oxide. In some embodiments,the aqueous solution or the first aqueous solution comprising thecalcium salt and the magnesium oxide is contacted with the CO₂ (ande.g., the NH₃ as in FIG. 2 or the second aqueous solution as in FIG. 3 )prior to and while subjecting the aqueous solution or the first aqueoussolution to the one or more precipitation conditions that favorformation of the composition comprising the vaterite and the magnesiumoxide. In some embodiments, the aqueous solution or the first aqueoussolution comprising the calcium salt and the magnesium oxide iscontacted with the CO₂ (and e.g., the NH₃ as in FIG. 2 or the secondaqueous solution as in FIG. 3 ) after subjecting the aqueous solution orthe first aqueous solution to the one or more precipitation conditionsthat favor formation of the composition comprising the vaterite and themagnesium oxide.

In some embodiments, the contacting of the aqueous solution or the firstaqueous solution comprising the calcium salt and the magnesium oxidewith the carbon dioxide and optionally the ammonia or the second aqueoussolution is achieved by contacting the aqueous solution or the firstaqueous solution to achieve and maintain a desired pH range, a desiredtemperature range, and/or desired divalent cation concentration using aconvenient protocol as described herein (the one or more precipitationconditions). In some embodiments, the systems include a precipitationreactor configured to contact the aqueous solution or the first aqueoussolution comprising the calcium salt and the magnesium oxide with thecarbon dioxide and optionally the ammonia from step A of the process orthe systems include a precipitation reactor configured to contact theaqueous solution or the first aqueous solution comprising the calciumsalt and the magnesium oxide with the second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, (optionally ammoniumcarbamate), or combinations thereof.

In some embodiments, the aqueous solution or the first aqueous solutioncomprising the calcium salt and the magnesium oxide may be placed in aprecipitation reactor, wherein the amount of the aqueous solution or thefirst aqueous solution comprising the calcium salt and the magnesiumoxide added is sufficient to raise the pH to a desired level (e.g., a pHthat induces precipitation of the precipitation material) such as pH7-9, pH 7-8.7, pH 7-8.5, pH 7-8, pH 7.5-8, pH 8-8.5, pH 8.5-9, pH 9-14,pH 10-14, pH 11-14, pH 12-14, or pH 13-14. In some embodiments, the pHof the aqueous solution or the first aqueous solution comprising thecalcium salt and the magnesium oxide when contacted with the carbondioxide and optionally the NH₃ or the second aqueous solution, ismaintained at between 7-9 or between 7-8.7 or between 7-8.5 or between7.5-8.5 or between 7-8, or between 7.6-8.5, or between 8-8.5, or between7.5-9.5 in order to form the composition comprising the vaterite and themagnesium oxide.

In some embodiments, the aqueous solution or the first aqueous solutionis immobilized in a column or bed (an example of a configuration of theprecipitation reactor). In such embodiments, water is passed through orover an amount of the calcium salt solution sufficient to raise the pHof the water to a desired pH or to a particular divalent cation (Ca′)concentration. In some embodiments, the aqueous solution or the firstaqueous solution may be cycled more than once, wherein a first cycle ofprecipitation removes primarily calcium carbonate minerals and leaves analkaline solution to which additional aqueous solution or the firstaqueous solution comprising the calcium salt and the magnesium oxide maybe added. The gaseous stream comprising the carbon dioxide andoptionally the NH₃, or the second aqueous solution when contacted withthe recycled solution of the aqueous solution, allows for theprecipitation of more calcium carbonate and/or bicarbonate compounds. Itwill be appreciated that, in these embodiments, the aqueous solutionfollowing the first cycle of precipitation may be contacted with thegaseous stream comprising the CO₂ and optionally the NH₃ (or with thesecond aqueous solution) before, during, and/or after the aqueoussolution or the first aqueous solution comprising the calcium salt andthe magnesium oxide has been added. In these embodiments, the water maybe recycled or newly introduced. As such, the order of addition of thegaseous stream comprising the CO₂ and optionally the NH₃ and the aqueoussolution or the first aqueous solution comprising the calcium salt andthe magnesium oxide may vary. For example, the aqueous solution or thefirst aqueous solution comprising the calcium salt and the magnesiumoxide may be added to, for example, brine, seawater, or freshwater,followed by the addition of the gaseous stream comprising the CO₂ andoptionally the NH₃, or the second aqueous solution. In another example,the gaseous stream comprising the CO₂ and optionally the NH₃, or thesecond aqueous solution may be added to, for example, brine, seawater,or freshwater, followed by the addition of the aqueous solution or thefirst aqueous solution comprising the calcium salt and the magnesiumoxide. In another example, the gaseous stream comprising the CO₂ andoptionally the NH₃, or the second aqueous solution may be added directlyto the aqueous solution or the first aqueous solution comprising thecalcium salt and the magnesium oxide.

The aqueous solution or the first aqueous solution comprising thecalcium salt and the magnesium oxide may be contacted with the gaseousstream comprising the CO₂ and optionally the NH₃ using any convenientprotocol. The contact protocols of interest include, but not limited to,direct contacting protocols (e.g., bubbling the gases through theaqueous solution or the first aqueous solution), concurrent contactingmeans (i.e., contact between unidirectional flowing gaseous and liquidphase streams), countercurrent means (i.e., contact between oppositelyflowing gaseous and liquid phase streams), and the like. As such,contact may be accomplished through use of infusers, bubblers, fluidicVenturi reactors, spargers, gas filters, sprays, trays, or packed columnreactors, and the like, in the precipitation reactor. In someembodiments, gas-liquid contact is accomplished by forming a liquidsheet of solution with a flat jet nozzle, wherein the gases and theliquid sheet move in countercurrent, co-current, or crosscurrentdirections, or in any other suitable manner. In some embodiments,gas-liquid contact is accomplished by contacting liquid droplets of thesolution having an average diameter of 500 micrometers or less, such as100 micrometers or less, with the gas source.

In some embodiments, substantially (e.g., 80% or more or 90% or 99.9% or100%) the entire gaseous CO₂ (from the calcination) and optionally NH₃waste stream produced by step A of the process illustrated in Figsherein is employed in the precipitation of the precipitation material.In some embodiments, a portion of the gaseous CO₂ and optionally NH₃waste stream is employed in the precipitation of the precipitationmaterial and may be 75% or less, such as 60% or less, and including 50%and less of the gaseous waste stream.

Any number of the gas-liquid contacting protocols described herein maybe utilized. Gas-liquid contact or the liquid-liquid contact iscontinued until the pH of the precipitation reaction mixture is optimum(various optimum pH values have been described herein to form thecomposition/precipitation material comprising e.g., the vaterite and themagnesium oxide), after which the precipitation reaction mixture isallowed to stir. The rate at which the pH drops may be controlled byaddition of more of the aqueous solution or the first aqueous solutioncomprising the calcium salt and the magnesium oxide during gas-liquidcontact or the liquid-liquid contact. In addition, additional aqueoussolution or the first aqueous solution may be added after sparging toraise the pH back to basic levels for precipitation of a portion or allof the precipitation material. In any case, the precipitation materialmay be formed upon removing protons from certain species in theprecipitation reaction mixture. The precipitation material comprisingcarbonates may then be separated and optionally, further processed.

The rate at which the pH drops may be controlled by addition ofadditional supernatant or the aqueous solution or the first aqueoussolution comprising the calcium salt and the magnesium oxide duringgas-liquid contact or the liquid-liquid contact. In addition, additionalsupernatant or the aqueous solution or the first aqueous solutioncomprising the calcium salt and the magnesium oxide may be added aftergas-liquid contact or the liquid-liquid contact to raise the pH back tobasic levels (e.g., between 7-9 or between 7-8.5 or between 7-8 orbetween 8-9) for precipitation of a portion or all of thecomposition/precipitation material.

In methods and systems provided herein, the aqueous solution produced bycontacting the aqueous solution or the first aqueous solution comprisingthe calcium salt and the magnesium oxide with the gaseous streamcomprising the CO₂ and optionally the NH₃ or the aqueous solutionproduced by contacting the first aqueous solution comprising the calciumsalt and the magnesium oxide with the second aqueous solution comprisingammonium bicarbonate, ammonium carbonate, ammonia, (optionally ammoniumcarbamate) or combinations thereof, is subjected to the one or more ofprecipitation conditions (step C in FIGS. 1-3 ) sufficient to producethe composition comprising the vaterite and the magnesium oxide and asupernatant (i.e., the part of the solution that is left over afterprecipitation of the composition/precipitation material). The one ormore precipitation conditions favor production of the compositioncomprising the vaterite and the magnesium oxide.

The one or more precipitation conditions include those that modulate theenvironment of the precipitation reaction mixture to produce the desiredcomposition comprising the vaterite and the magnesium oxide. Such one ormore precipitation conditions, that can be used in the method and systemaspects and embodiments described herein, suitable to form compositioncomprising the vaterite and the magnesium oxide include, but not limitedto, temperature, pH, pressure, ion ratio, precipitation rate, presenceof additive, presence of ionic species, concentration of additive andionic species, stirring, residence time, mixing rate, forms of agitationsuch as ultrasonics, presence of seed crystals, catalysts, membranes, orsubstrates, dewatering, drying, ball milling, etc. In some embodiments,the average particle size of the vaterite may also depend on the one ormore precipitation conditions used in the precipitation of thecomposition.

For example, the temperature of the precipitation reaction may be raisedto a point at which an amount suitable for precipitation of the desiredcomposition occurs. In such embodiments, the temperature of theprecipitation reaction may be raised to a value, such as from 20° C. to60° C., and including from 25° C. to 60° C.; or from 30° C. to 60° C.;or from 35° C. to 60° C.; or from 40° C. to 60° C.; or from 50° C. to60° C.; or from 25° C. to 50° C.; or from 30° C. to 50° C.; or from 35°C. to 50° C.; or from 40° C. to 50° C.; or from 25° C. to 40° C.; orfrom 30° C. to 40° C.; or from 25° C. to 30° C. In some embodiments, thetemperature of the precipitation reaction may be raised using energygenerated from low or zero carbon dioxide emission sources (e.g., solarenergy source, wind energy source, hydroelectric energy source, wasteheat from the flue gases of the carbon emitter, etc.).

The pH of the precipitation reaction may also be raised to an amountsuitable for the precipitation of the desired composition comprising thevaterite and the magnesium oxide. In such embodiments, the pH of theprecipitation reaction may be raised to alkaline levels forprecipitation. In some embodiments, the pH of the aqueous solution orthe first aqueous solution comprising the calcium salt and the magnesiumoxide that is contacted with the gaseous stream comprising the carbondioxide gas and optionally the NH₃ gas (or with the second aqueoussolution) has an effect on the formation of the composition comprisingthe vaterite and the magnesium oxide. In some embodiments, theprecipitation conditions include conducting the precipitation step ofthe gaseous stream comprising the carbon dioxide gas and optionally theNH₃ gas (or the second aqueous solution) with the aqueous solution orthe first aqueous solution comprising the calcium salt and the magnesiumoxide at pH higher than 7 or pH of 8 or pH of between 7.1-8.5 or pH ofbetween 7.5-8 or between 7.5-8.5 or between 8-8.5 or between 8-9 orbetween 7.6-8.4, in order to form the composition/precipitationmaterial. The pH may be raised to pH 9 or higher, such as pH 10 orhigher, including pH 11 or higher or pH 12.5 or higher.

Adjusting major ion ratios during precipitation may influence the natureof the precipitation material. Major ion ratios may have considerableinfluence on polymorph formation. For example, as the magnesium:calciumratio in the water increases, aragonite become the major polymorph ofcalcium carbonate in the precipitation material over low-magnesiumvaterite.

Precipitation rate may also have an effect on the composition formation,with the most rapid precipitation rate achieved by seeding the solutionwith a desired phase. Without seeding, rapid precipitation may beachieved by rapidly increasing the pH of the precipitation reactionmixture, which may result in more amorphous constituents. The higher thepH, the more rapid is the precipitation, which may result in a moreamorphous precipitation material.

Residence time of the precipitation reaction after contacting theaqueous solution or the first aqueous solution with the gaseous streamcomprising the carbon dioxide gas and optionally the NH₃ gas (or withthe second aqueous solution) may also have an effect on theprecipitation material formation. For example, in some embodiments, alonger residence time may result in transformation of the vaterite tothe aragonite/calcite within the reaction mixture. In some embodiments,too short residence time may result in an incomplete formation of thevaterite in the reaction mixture. Therefore, the residence time may becritical to the precipitation of the vaterite. Further, the residencetime may also affect the particle size of the precipitate. For example,too long residence time may result in the agglomeration of the particlesforming large size particles. Therefore, in some embodiments, theresidence time of the reaction is between about 5-60 minutes, or betweenabout 5-15 minutes, or between about 10-60 minutes, or between about15-60 min, or between about 15-45 min, or between about 15-30 min, orbetween about 30-60 min.

In some embodiments, the one or more precipitation conditions to producethe composition from the precipitation reaction may include, as above,the temperature and pH, as well as, in some instances, theconcentrations of additives and ionic species in the water. Theadditives have been described herein below. The presence of theadditives and the concentration of the additives may also favorformation of the composition comprising the vaterite and the magnesiumoxide. In some embodiments, a middle chain or long chain fatty acidester may be added to the aqueous solution or the first aqueous solutionduring the precipitation. Examples of fatty acid esters include, withoutlimitation, cellulose such as carboxymethyl cellulose, sorbitol, citratesuch as sodium or potassium citrate, stearate such as sodium orpotassium stearate, phosphate such as sodium or potassium phosphate,sodium tripolyphosphate, hexametaphosphate, EDTA, or combinationsthereof. In some embodiments, a combination of stearate and citrate maybe added during the precipitation step of the process to form thecomposition comprising the vaterite and the MgO.

The one or more precipitation conditions may also include factors suchas mixing rate, forms of agitation such as ultrasonics, and the presenceof seed crystals, catalysts, membranes, or substrates. In someembodiments, the one or more precipitation conditions includesupersaturated conditions, temperature, pH, and/or concentrationgradients, or cycling or changing any of these parameters. The protocolsemployed to prepare the precipitation material may be batch, semi-batch,or continuous protocols. The one or more precipitation conditions may bedifferent to produce the precipitation material in a continuous flowsystem compared to a semi-batch or batch system.

In some embodiments, the gas leaving the precipitation reactor (shown as“scrubbed gas” at step C in FIGS. 1-3 ) passes to a gas treatment unitfor a scrubbing process. The mass balance and equipment design for thegas treatment unit may depend on the properties of the gases. In someembodiments, the gas treatment unit may incorporate an acid scrubber,such as, e.g., hydrochloric acid (HCl) scrubber or sulfuric acid (H₂SO₄)scrubber for recovering the small amounts of NH₃ in the gas exhauststream that may be carried from the CO₂ absorption, precipitation stepby the gas. The NH₃ may be captured by the HCl solution through:NH₃(g)+HCl(aq)→NH₄Cl(aq)

The NH₄Cl (aq) from the HCl scrubber or the NH₄SO₄ (aq) from the H₂SO₄scrubber may be recycled to the dissolution step A.

In some embodiments, the gas exhaust stream comprising ammonia (shown as“scrubbed gas” in FIGS. 1-3 ) may be subjected to a scrubbing processwhere the gas exhaust stream comprising ammonia is scrubbed with thecarbon dioxide from the industrial process and water to produce asolution of ammonia. The inlets for the scrubber may be carbon dioxide(CO_(2(g))), the reactor gas exhaust containing ammonia (NH_(3(g))), andfresh makeup water (or some other dilute water stream). The outlet maybe a slipstream of the scrubber's recirculating fluid (e.g.H₃N—CO_(2(aq)) or carbamate), which may optionally be returned back tothe main reactor for contacting with the carbon dioxide andprecipitation. The pH of the system may be controlled by regulating theflow rate of CO_(2(g)) into the scrubber. The conductivity of the systemmay be controlled by addition of dilute makeup water to the scrubber.Volume may be maintained constant by using a level detector in thescrubber or it's reservoir. While ammonia is a basic gas, the carbondioxide gases are acidic gases. In some embodiments, the acidic andbasic gases may ionize each other to increase their solubilities.

Without being limited by any theory, it is contemplated that thefollowing reaction may take place in the scrubber:NH₃(aq)+CO₂(aq)+H₂O→HCO₃ ⁻+NH₄ ⁺

The aqueous solution or the first aqueous solution comprising thecalcium salt and the magnesium oxide when contacted with the gaseousstream comprising the CO₂ gas and optionally the NH₃ gas or with thesecond aqueous solution under the one or more precipitation conditionsresults in the precipitation of the composition comprising the vateriteand the magnesium oxide. The one or more precipitation conditions thatresult in the formation of the composition comprising the vaterite andthe magnesium oxide in this process have been described herein.

In some embodiments, the vaterite in the composition may be formed undersuitable conditions so that the vaterite is reactive and transforms tothe aragonite and/or the calcite upon dissolution-precipitation process(during cementation) in the water. The magnesium oxide transforms to themagnesium hydroxide during the cementation process. The aragonite and/orcalcite along with the magnesium hydroxide may impart one or more uniquecharacteristics to the cemented product including, but not limited to,high compressive strength, complex microstructure network, neutral pH,filling of the porosity of the aragonite and/or calcite network with themagnesium hydroxide, etc. The composition comprising the vaterite andthe magnesium oxide (either as part of the composition throughout theprocess or as added solids comprising the magnesium oxide, as describedherein) undergoes transformation to the aragonite and/or the calcite andsets and hardens into cementitious products (shown as products (A) inFIGS. 1-3 ). The non-removal of the magnesium oxide solid in the processto form the composition comprising the vaterite and the magnesium oxideprovides an additional advantage of one less step of removal of thesolids, eliminating a potential waste stream thereby increasing theefficiency and improving the economics of the process.

In some embodiments, the methods and systems provided herein furtherinclude separating the composition/precipitation material (step D inFIGS. 1-3 ) from the aqueous solution by dewatering to form the calciumcarbonate and the magnesium oxide cake (as shown in FIGS. 1-3 ). Thecalcium carbonate and the magnesium oxide cake may be subjectedoptionally to rinsing, and optionally drying (step E in FIGS. 1-3 ). Thedrying of the cake form of the composition comprising the calciumcarbonate and the magnesium oxide results in the formation of the powderform of the composition comprising the calcium carbonate and themagnesium oxide which may then be used to make cementitious ornon-cementitious products (shown as products (B) in FIGS. 1-3 ). In someembodiments, the calcium carbonate and the magnesium oxide cake maycontain impurities (e.g., 1-2% by weight or more) of ammonium (NH₄ ⁺)ions, sulfur ions, and/or chloride (Cl⁻) ions. While rinsing of thecalcium carbonate and the magnesium oxide cake may remove some or all ofthe ammonium salts and/or sulfur compounds, it may result in a diluteconcentration of ammonium salts (in the supernatant) which may needconcentrating before recycling it back to the process.

The methods and systems provided herein may result in residualN-containing inorganic or N-containing organic salt, e.g., residualammonium salt remaining in the supernatant solution as well as in theprecipitate itself after the formation of the precipitate. The residualN-containing inorganic or the residual N-containing organic salt, e.g.residual ammonium salt (e.g. residual NH₄Cl, or residual NH₄CH₃CO₂(ammonium acetate)) as used herein includes any salt that may be formedby ammonium ions and anions present in the solution including, but notlimited to halogen ions such as chloride ions, acetate ions, nitrate ornitrite ions, and sulfur ions such as, sulfate ions, sulfite ions,thiosulfate ions, hydrosulfide ions, and the like. In some embodiments,the residual N-containing inorganic salt comprises ammonium halide,ammonium acetate, ammonium sulfate, ammonium sulfite, ammoniumhydrosulfide, ammonium thiosulfate, ammonium nitrate, ammonium nitrite,or combinations thereof. Various methods have been provided herein toremove and optionally recover the residual salt from the supernatantsolution as well as the precipitate. In some embodiments, thesupernatant solution further comprising the N-containing inorganic orN-containing organic salt, e.g., residual ammonium salt (e.g., residualNH₄Cl, or residual NH₄CH₃CO₂), is recycled back to the dissolutionreactor for the dissolution of the mixture (to step A in FIGS. 1-3 ).

The residual N-containing inorganic or N-containing organic saltsolution, e.g., residual ammonium salt solution (e.g., residual NH₄Cl orresidual NH₄CH₃CO₂) obtained from the dewatering as well as the rinsingstream may optionally be concentrated before being recycled back for thedissolution of the mixture. Additional base, such as e.g., ammoniumchloride and/or ammonia (anhydrous or aqueous solution) may be added tothe recycled solution to make up for the loss of the ammonium chlorideduring the process and bring the concentration of ammonium chloride tothe optimum level.

In some embodiments, the residual N-containing inorganic or N-containingorganic salt solution, e.g., residual ammonium salt solution (e.g.residual NH₄Cl or residual NH₄CH₃CO₂), as illustrated in FIGS. 1-3 , maybe recovered from the supernatant aqueous solution and concentratedusing recovery process, such as, but not limited to, thermaldecomposition, pH adjustment, reverse osmosis, multi-stage flashdistillation, multi-effect distillation, vapor recompression,distillation, or combinations thereof. The systems configured to carryout these processes are available commercially. For example, the pH ofthe solution may be raised (e.g., with a strong base like NaOH). Thismay shift the equilibrium towards volatile ammonia (NH₃(aq)/NH₃(g)).Rates and total removal could both be improved by heating the solution.

In some embodiments, the residual N-containing inorganic or N-containingorganic salt solution, e.g., residual ammonium salt solution (e.g.,residual NH₄Cl or residual NH₄CH₃CO₂) may be separated and recoveredfrom the precipitate by the thermal decomposition process. This processmay be incorporated in the processes illustrated in FIGS. 1-3 at theseparation of the composition comprising the vaterite and the magnesiumoxide (step D) and/or after the step of the dried powder (step E).

Typically, at 338° C., solid NH₄Cl may decompose into ammonia (NH₃) andhydrogen chloride (HCl) gases. While at 840° C., solid CaCO₃ decomposesto calcium oxide (CaO) solid and carbon dioxide (CO₂) gas.NH₄Cl_((s))←→NH_(3(g))+HCl_((g))CaCO_(3(s))←→CaO_((s))+CO_(2(g))

In some embodiments, the residual ammonium salt in the precipitateand/or dried powder such as, but not limited to, ammonium chloride,ammonium acetate, ammonium sulfate, ammonium sulfite, ammoniumhydrosulfide, ammonium thiosulfate, ammonium nitrate, ammonium nitrite,or combinations thereof may be removed by thermal decomposition at atemperature between 80-840° C. This may be done either during the normalfilter cake drying process and/or as a second post-drying heattreatment. A temperature range is desirable that decomposes residualammonium salts in the precipitation while preserving the cementitiousproperties of the vaterite in the composition such that the vateritestays as the vaterite after heating, and after combination with water,successfully transforms to the aragonite and/or the calcite to form thecementitious products.

In some embodiments of the foregoing aspect and embodiments, the step ofremoving and optionally recovering the residual N-containing inorganicor N-containing organic salt, such as e.g. the ammonium salt from theprecipitation material comprises heating the precipitation materialbetween about 80-380° C. or between about 100-360° C. or between about150-360° C. or between about 200-360° C. or between about 250-360° C. orbetween about 300-360° C. or between about 150-200° C. or between about100-200° C. or between about 200-300° C. or between about 300-350° C. orbetween about 310-345° C. or between about 320-345° C. or between about330-345° C. or between about 300-345° C., to evaporate the residualN-containing inorganic or N-containing organic salt from theprecipitation material with optional recovery by condensation of theresidual N-containing inorganic or N-containing organic salt.

In some embodiments of the foregoing aspect and embodiments, the step ofremoving and optionally recovering the residual N-containing inorganicor N-containing organic salt, such as e.g. the residual ammonium saltfrom the precipitation material comprises heating the precipitationmaterial, for a duration of more than about 10 min or of more than about15 min or for than about 5 min or of between about 10 min to about 1hour or of between about 10 min to about 1.5 hour or of between about 10min to about 2 hours or of between about 10 min to about 5 hours or ofbetween about 10 min to about 10 hours.

In some embodiments, the composition/precipitation material is dewatered(to remove the supernatant aqueous solution) and dried to remove water(e.g., by heating at about or above 100° C.) before subjecting thecomposition to the heating step as above to remove and optionallyrecover the residual N-containing inorganic or N-containing organicsalt, e.g., residual ammonium salt. In some embodiments, the compositionis partially dewatered (to remove bulk of the supernatant aqueoussolution) and partially dried to remove water (or avoid the drying step)before subjecting the composition to the heating step to remove andoptionally recover the residual N-containing inorganic or N-containingorganic salt, e.g., residual ammonium salt. In some embodiments, theammonium salt evaporates from the precipitation material in a formcomprising ammonia gas, hydrogen chloride gas, chlorine gas, orcombinations thereof. Applicants have found that in some embodiments,maintaining a combination of the amount of temperature and duration ofheating may be critical to removing the ammonium salt from theprecipitation material yet preserving the cementitious properties of thevaterite. The cementitious products, thus formed, possess minimal or nochloride content and have no foul smell of ammonia or sulfur. In someembodiments, the chloride content is around or below acceptable ASTMstandards for the cementitious products.

In some embodiments, the above recited temperature conditions optionallycoupled with duration of heating, may be combined with pressureconditions that provide a driving force to improve the thermodynamics ofthe decomposition of the residual N-containing inorganic or N-containingorganic salt, e.g., the residual ammonium salt. For example, the heatingof the precipitation material may be carried out in a system in whichthe headspace is at a pressure lower than atmospheric pressure. Thepressure lower than the atm pressure may create a driving force forheating reaction that involves gas phase products (such as, but notlimited to, ammonia gas, hydrogen chloride gas, chlorine gas, orcombinations thereof), by reducing the partial pressure of the reactantin the vapor phase. Another advantage of operating under reducedpressure or vacuum may be that at lower pressure some sublimationreactions may occur at lower temperatures thereby improving the energyrequirements of the heating reaction.

In some embodiments of the above described thermal decompositionprocess, the separated ammonium chloride in the form of the ammonia andthe HCl gases, may be recovered for reuse by either recrystallization ofthe combined thermally evolved gases or by absorbing the gases into anaqueous medium. Both mechanisms may result in the NH₄Cl product that maybe concentrated enough for reuse in the processes as shown in FIGS. 1-3.

In some embodiments, the ammonium salt may be separated and recovered inthe above described process by pH adjusted evolution of the NH₃ gas fromthe ammonium salt. This process may be incorporated in the processesillustrated in FIGS. 1-3 at the separation of the vaterite and themagnesium oxide cake. The final pH of the water in the filter cake maytypically be about 7.5. At this pH, NH₄ ⁺ (pKa=9.25) may be thepredominant species. Increasing the pH of this water may drive the acidbase equilibrium toward NH₃ gas, as described in the following equation:NH₄ ⁺←→H⁺+NH_(3(g))

Any source of alkalinity may be used to increase the pH of the filtercake water. In some embodiments, the aqueous solution of the calciumoxide and/or hydroxide or the lime slurry may provide the source of highalkalinity. In some embodiments, the aqueous fraction of the lime may beintegrated into the rinsing stage of the dewatering process (e.g.,filter cake step) to raise the pH of the system and drive the evolutionof NH₃ gas. As ammonia has substantial solubility in water, heat and/orvacuum pressure may be applied to drive the equilibrium further towardthe gaseous phase. The ammonia may be recovered for reuse by eitherrecrystallization of the ammonia with chloride or by absorbing theammonia into an aqueous medium. Both mechanisms may result in theammonia solution or the NH₄Cl product that may be concentrated enoughfor reuse in the processes described in FIGS. 1-3 .

The cake composition comprising the vaterite and the magnesium oxide maybe sent to the dryer (step E in FIGS. 1-3 ) to form the powdercomposition comprising the vaterite and the magnesium oxide. The powderform of the composition may be used further in applications to form theproducts, as described herein. The cake may be dried using any dryingtechniques known in the art such as, but not limited to fluid bed dryeror swirl fluidizer. The resulting solid powder may be then mixed withadditives to make different products described herein. In someembodiments, the slurry form with reduced water or the cake form of thecomposition is directly used to form the products, such as theconstruction panel, or the concrete, or the aggregate, etc., asdescribed herein.

In the systems provided herein, the separation or the dewatering step Dmay be carried out on the separation station. The composition comprisingthe vaterite and the magnesium oxide may be stored in the supernatantfor a period of time following the precipitation and prior to theseparation. For example, the composition may be stored in thesupernatant for a period of time ranging from few min to hours to 1 to1000 days or longer, such as 1 to 10 days or longer, at a temperatureranging from 1° C. to 40° C., such as 20° C. to 25° C. The separation orthe dewatering may be achieved using any of a number of convenientapproaches, including draining (e.g., gravitational sedimentation of theprecipitation material followed by draining), decanting, filtering(e.g., gravity filtration, vacuum filtration, filtration using forcedair), centrifuging, pressing, or any combination thereof. Separation ofthe bulk water from the composition produces the wet cake of thecomposition, or the dewatered composition. Liquid-solid separator suchas Epuramat's Extrem-Separator (“ExSep”) liquid-solid separator, XeroxPARC's spiral concentrator, or a modification of either of Epuramat'sExSep or Xerox PARC's spiral concentrator, may be useful for theseparation of the composition from the precipitation reaction.

In some embodiments, the resultant dewatered composition such as the wetcake material (after e.g., thermally removing the N-containing salt) maybe directly used to make the products (A) described herein. For example,the wet cake of the composition comprising the vaterite and themagnesium oxide is mixed with the one or more additives, describedherein, and is spread out on the conveyer belt where the vateritetransforms to the aragonite and/or the calcite, the magnesium oxidetransforms to the magnesium hydroxide, and the mixture sets and hardens.The hardened material is then cut into desired shapes such as boards orpanels described herein. In some embodiments, the wet cake is pouredonto a sheet of paper on top of the conveyer belt. Another sheet ofpaper may be put on top of the wet cake which is then pressed to removeexcess water. After the setting and hardening of the composition (thevaterite transformation to the aragonite and/or the calcite and themagnesium oxide transformation to the magnesium hydroxide), the materialis cut into desired shapes, such as, cement siding boards and drywalletc. In some embodiments, the amount of the one or more additives may beoptimized depending on the desired time required for the transformationof the vaterite to the aragonite and/or the calcite (described below).For example, for some applications, it may be desired that the materialtransforms rapidly and in certain other instance, a slow transformationmay be desired. In some embodiments, the wet cake may be heated on theconveyer belt to hasten the transformation of the vaterite to thearagonite and/or the calcite and the magnesium oxide to the magnesiumhydroxide. In some embodiments, the wet cake may be poured in the moldsof desired shape and the molds are then heated in the autoclave tohasten the transformation of the vaterite to the aragonite and/or thecalcite and the magnesium oxide to the magnesium hydroxide (andoptionally to remove residual salt). Accordingly, the continuous flowprocess, batch process or semi-batch process, all are well within thescope of the invention.

In some embodiments, the composition comprising the vaterite and themagnesium oxide, once separated from the precipitation reaction, iswashed with fresh water, and then placed into a filter press to producea filter cake with 30-60% solids. This filter cake is then mechanicallypressed in a mold, using any convenient means, e.g., a hydraulic press,at adequate pressures, e.g., ranging from 5 to 5000 psi, such as 1000 to5000 psi, to produce a formed solid (where the vaterite has transformedto the aragonite and/or the calcite and the magnesium oxide hastransformed to the magnesium hydroxide), e.g., a rectangular brick.These resultant solids are then cured, e.g., by placing outside andstoring, by placing in a chamber wherein they are subjected to highlevels of humidity and heat, etc. These resultant cured solids are thenused as building materials themselves or crushed to produce theaggregate.

In processes involving the use of temperature and pressure, thedewatered cake may be dried. The cake is then exposed to a combinationof rewatering, and elevated temperature and/or pressure for a certaintime. The combination of the amount of water added back, thetemperature, the pressure, and the time of exposure, as well as thethickness of the cake, can be varied according to composition of thestarting material and the desired results.

A number of different ways of exposing the material to temperature andpressure are described herein; it will be appreciated that anyconvenient method may be used. Thickness and size of the cake may beadjusted as desired; the thickness can vary in some embodiment from 0.05inch to 5 inches, e.g., 0.1-2 inches, or 0.3-1 inch. In some embodimentsthe cake may be 0.5 inch to 6 feet or even thicker. The cake is thenexposed to elevated temperature and/or pressure for a given time, by anyconvenient method, for example, in a platen press using heated platens.The heat to elevate the temperature, e.g., for the platens, may beprovided, e.g., by heat from an industrial waste gas stream such as aflue gas stream. The temperature may be any suitable temperature; ingeneral, for a thicker cake a higher temperature is desired; examples oftemperature ranges are 40-150° C., e.g., 60-120° C., such as 70-110° C.,or 80-100° C. Similarly, the pressure may be any suitable pressure toproduce the desired results; exemplary pressures include 1000-100,000pounds per square inch (psi), including 2000-50,000 psi, or 2000-25,000psi, or 2000-20,000 psi, or 3000-5000 psi. Finally, the time that thecake is pressed may be any suitable time, e.g., 1-100 seconds, or 1-100minute, or 1-50 minutes, or 2-25 minutes, or 1-10,000 days. Theresultant hard tablet may optionally then cure, e.g., by placing outsideand storing, by placing in a chamber wherein they are subjected to highlevels of humidity and heat, etc. These hard tablets, optionally cured,are then used as building materials themselves or crushed to produceaggregate.

Another method of providing the temperature and the pressure is the useof a press. A suitable press, e.g., a platen press, may be used toprovide pressure at the desired temperature (using heat supplied, e.g.,by a flue gas or by other steps of the process to produce a precipitate,e.g., from an electrochemical process) for a desired time. A set ofrollers may be used in similar fashion.

Another way to expose the cake to elevated temperature and pressure isby means of an extruder, e.g., a screw-type extruder. The barrel of theextruder can be outfitted to achieve an elevated temperature, e.g., byjacketing; this elevated temperature can be supplied by, e.g., fluegases or the like. Extrusion may be used as a means of pre-heating anddrying the feedstock prior to a pressing operation. Such pressing can beperformed by means of a compression mold, via rollers, via rollers withshaped indentations (which can provide virtually any shape of aggregatedesired), between a belt which provides compression as it travels, orany other convenient method. Alternatively, the extruder may be used toextrude material through a die, exposing the material to pressure as itis forced through the die, and giving any desired shape. In someembodiments, the composition comprising the vaterite and the magnesiumoxide is mixed with the fresh water and then placed into the feedsection of a rotating screw extruder. The extruder and/or the exit diemay be heated to further assist in the process. The turning of the screwconveys the material along its length and compresses it as the flitedepth of the screw decreases. The screw and barrel of the extruder mayfurther include vents in the barrel with decompression zones in thescrew coincident with the barrel vent openings. Particularly in the caseof a heated extruder, these vented areas allow for the release of steamfrom the conveyed mass, removing water from the material.

The screw conveyed material is then forced through a die section whichfurther compresses the material and shapes it. Typical openings in thedie can be circular, oval, square, rectangular, trapezoidal, etc.,although any shape which the final aggregate is desired in could be madeby adjusting the shape of the opening. The material exiting the die maybe cut to any convenient length by any convenient method, such as by afly knife. Use of a heated die section may further assist in theformation of the product by accelerating the transition of the carbonatemineral to a hard, stable form. Heated dies may also be used in the caseof binders to harden or set the binder. Temperatures of 100° C. to 600°C. are commonly used in the heated die section.

In yet other embodiments, the composition comprising the vaterite andthe magnesium oxide may be employed for in situ or form-in-placestructure fabrication. For example, roads, paved areas, or otherstructures may be fabricated from the composition by applying a layer ofthe composition, e.g., as described above, to a substrate, e.g., ground,roadbed, etc., and then hydrating the composition, e.g., by allowing itto be exposed to naturally applied water, such as in the form of rain,or by irrigation. Hydration solidifies the composition (the vateritetransformation to the aragonite and/or the calcite and the magnesiumoxide transformation to the magnesium hydroxide) into a desired in situor form-in-place structure, e.g., road, paved over area, etc. Theprocess may be repeated, e.g., where thicker layers of in-situ formedstructures are desired.

In some embodiments, the production of the composition and the productsis carried out in the same facility. In some embodiments, thecomposition is produced in one facility and is transported to anotherfacility to make the end product. The composition may be transported inthe slurry form, the wet cake form, or the dry powder form.

In some embodiments, the resultant dewatered composition obtained fromthe separation station is dried at the drying station to produce thepowder form of the composition comprising vaterite and the magnesiumoxide. Drying may be achieved by air-drying the composition. In certainembodiments, the drying is achieved by freeze-drying (i.e.,lyophilization), wherein the composition is frozen, the surroundingpressure is reduced, and enough heat is added to allow the frozen waterin the composition to sublime directly into gas. In yet anotherembodiment, the composition is spray-dried to dry the composition,wherein the liquid containing the composition is dried by feeding itthrough a hot gas (such as the gaseous waste stream from the powerplant), and wherein the liquid feed is pumped through an atomizer into amain drying chamber and a hot gas is passed as a co-current orcounter-current to the atomizer direction. Depending on the particulardrying protocol of the system, the drying station may include afiltration element, freeze-drying structure, spray-drying structure,etc. In some embodiments, the precipitate may be dried by fluid beddryer. In certain embodiments, waste heat from a power plant or similaroperation may be used to perform the drying step when appropriate. Forexample, in some embodiments, the dry product is produced by the use ofelevated temperature (e.g., from power plant waste heat), pressure, or acombination thereof. Following the drying of the composition, thematerial may be then subjected to heating at elevated temperatures toremove the residual N-containing salts, e.g., the residual ammoniumsalts as described herein.

The resultant supernatant of the precipitation process or slurry of thecomposition may also be processed as desired. For example, thesupernatant or slurry may be returned to the aqueous solution, or thefirst aqueous solution, or to another location. In some embodiments, thesupernatant may be contacted with the gaseous stream comprising CO₂ andoptionally ammonia gas, as described herein, to sequester additionalCO₂. For example, in embodiments in which the supernatant is to bereturned to the precipitation reactor, the supernatant may be contactedwith the gaseous stream of CO₂ and optionally the ammonia gas in amanner sufficient to increase the concentration of carbonate ion presentin the supernatant. As described above, contact may be conducted usingany convenient protocol. In some embodiments, the supernatant has analkaline pH, and contact with the CO₂ gas is carried out in a mannersufficient to reduce the pH to a range between pH 5 and 9, pH 6 and 8.5,or pH 7.5 to 8.7.

In some embodiments, the composition produced by methods providedherein, is employed as the building material (e.g., a constructionmaterial for some type of man-made structure such as buildings, roads,bridges, dams, and the like), such that CO₂ is effectively sequesteredin the built environment. Any man-made structure, such as foundations,parking structures, houses, office buildings, commercial offices,governmental buildings, infrastructures (e.g., pavements; roads;bridges; overpasses; walls; footings for gates, fences and poles; andthe like) is considered a part of the built environment. Mortars finduse in binding construction blocks (e.g., bricks) together and fillinggaps between construction blocks. Mortars can also be used to fixexisting structure (e.g., to replace sections where the original mortarhas become compromised or eroded), among other uses.

In some embodiments, the powder form of the composition comprising thevaterite and the magnesium oxide is employed as cement, where thevaterite transforms to the aragonite and/or the calcite (thedissolution-re-precipitation process) and the magnesium oxide transformsto the magnesium hydroxide and sets and hardens after combining withwater.

In some embodiments, the aggregate is produced from the composition. Insuch embodiments, where the drying process produces particles of thedesired size, little if any additional processing is required to producethe aggregate. In yet other embodiments, further processing of thecomposition is performed in order to produce the desired aggregate. Forexample, the composition may be combined with fresh water in a mannersufficient to cause the composition to form a solid product, where thevaterite transforms to the aragonite and/or the calcite (thedissolution-re-precipitation process) and the magnesium oxide transformsto the magnesium hydroxide. By controlling the water content of the wetmaterial, the porosity, and eventual strength and density of the finalaggregate may be controlled. Typically, the wet cake may be 40-60 volume% water. For denser aggregates, the wet cake may be <50% water, for lessdense cakes, the wet cake may be >50% water. After hardening, theresultant solid product may then be mechanically processed, e.g.,crushed or otherwise broken up and sorted to produce the aggregate ofthe desired characteristics, e.g., size, particular shape, etc. In theseprocesses the setting and mechanical processing steps may be performedin a substantially continuous fashion or at separate times. In certainembodiments, large volumes of the composition may be stored in the openenvironment where the composition is exposed to the atmosphere. For thesetting step, the composition may be irrigated in a convenient fashionwith fresh water or allowed to be rained on naturally in order toproduce the set product. The set product may then be mechanicallyprocessed as described above. Following production of the composition,the composition is processed to produce the desired aggregate. In someembodiment the composition may be left outdoors, where rainwater can beused as the freshwater source, to cause the meteoric water stabilizationreaction to occur, hardening the composition to form the aggregate.

Typically, upon precipitation of the calcium carbonate, amorphouscalcium carbonate (ACC) may initially precipitate and transform into oneor more of its three more stable phases (the vaterite, the aragonite, orthe calcite). A thermodynamic driving force may exist for thetransformation from unstable phases to more stable phases. For thisreason, calcium carbonate phases transform in the order: ACC tovaterite, aragonite, and calcite where intermediate phases may or maynot be present. During this transformation, excesses of energy arereleased, as exhibited in FIG. 5 . This intrinsic energy may beharnessed to create a strong aggregation tendency and surfaceinteractions that may lead to agglomeration and setting or cementing. Itis to be understood that the values reported in FIG. 5 are well known inthe art and may vary.

The methods and systems provided herein produce or isolate thecomposition comprising the vaterite and the magnesium oxide thattransforms to the aragonite form and/or the calcite form containingmagnesium hydroxide upon dissolution-re-precipitation. The aragoniteform may or may not convert further to more stable calcite form. Theproduct containing the aragonite and/or the calcite form containing themagnesium hydroxide shows one or more unexpected properties, includingbut not limited to, high compressive strength, high porosity (lowdensity or light weight), neutral pH (useful as artificial reefdescribed below), microstructure network, etc.

Other minor polymorph forms of calcium carbonate that may be present inthe carbonate containing precipitation material in addition to thevaterite include, but not limited to, amorphous calcium carbonate,aragonite, calcite, a precursor phase of vaterite, a precursor phase ofaragonite, an intermediary phase that is less stable than calcite,polymorphic forms in between these polymorphs or combination thereof.

The vaterite may be present in monodisperse or agglomerated form, andmay be in spherical, ellipsoidal, plate like shape, or hexagonal system.The vaterite typically has a hexagonal crystal structure and formspolycrystalline spherical particles upon growth. The precursor form ofthe vaterite comprises nanoclusters of the vaterite and the precursorform of the aragonite comprises sub-micron to nanoclusters of thearagonite needles. The aragonite, if present in the composition alongwith the vaterite, may be needle shaped, columnar, or crystals of therhombic system. The calcite, if present in the composition along withthe vaterite, may be cubic, spindle, or crystals of hexagonal system. Anintermediary phase that is less stable than the calcite may be a phasethat is between the vaterite and the calcite, a phase between precursorof the vaterite and the calcite, a phase between the aragonite and thecalcite, and/or a phase between precursor of the aragonite and thecalcite.

The transformation between the calcium carbonate polymorphs may occurvia solid-state transition, may be solution mediated, or both. In someembodiments, the transformation is solution-mediated as it may requireless energy than the thermally activated solid-state transition. Thevaterite is metastable and the difference in thermodynamic stability ofcalcium carbonate polymorphs may be manifested as a difference insolubility, where the least stable phases are the most soluble.Therefore, the vaterite may dissolve readily in solution and transformfavorably towards a more stable polymorph, such as the aragonite and/orthe calcite. In a polymorphic system like calcium carbonate, two kineticprocesses may exist simultaneously in solution: dissolution of themetastable phase and growth of the stable phase. In some embodiments,the aragonite crystals and/or the calcite crystals may be growing whilethe vaterite is undergoing dissolution in the aqueous medium.

In some embodiments of the compositions, methods and systems providedherein, the combination of the vaterite and the magnesium oxide resultsin the activation of the vaterite to the aragonitic pathway and not thecalcite pathway during dissolution-re-precipitation process. In someembodiments, the vaterite containing composition is activated in such away that after the dissolution-re-precipitation process, the aragoniteformation is enhanced and the calcite formation is suppressed. Theactivation of the vaterite containing composition may also result incontrol over the aragonite formation and crystal growth. This selectionand activation of the vaterite in the composition to only to thearagonite and not the calcite may be facilitated by the presence ofmagnesium oxide. As described herein before, the magnesium oxide may notjust control the transformation of the vaterite to the aragonite duringsetting and hardening, but itself converts to magnesium hydroxidefilling and binding with the aragonitic needles, thereby providing astable, durable, and hard material.

It is to be understood that the magnesium hydroxide may fully orpartially bind with the aragonitic needles or the calcite and it is notnecessary that all the magnesium hydroxide is bonded with the needles orthe calcite.

In some embodiments of the compositions, methods and systems providedherein, the combination of the vaterite and the magnesium oxide resultsin the activation of the vaterite to the calcite pathway duringdissolution-re-precipitation process. The process may be driven in sucha way that the vaterite transforms to the calcite along with themagnesium oxide transformation to the magnesium hydroxide. The magnesiumhydroxide fills and binds with the calcite, thereby providing a stable,durable, and hard material.

In some embodiments of the compositions, methods and systems providedherein, the combination of the vaterite and the magnesium oxide resultsin the activation of the vaterite to both the aragonite and the calcitepathway during dissolution-re-precipitation process. The process may bedriven in such a way that the vaterite transforms to the aragonite andthe aragonite partially or fully transforms to the calcite along withthe magnesium oxide transformation to the magnesium hydroxide. Themagnesium hydroxide fills and binds with the aragonite as well as thecalcite, thereby providing a stable, durable, and hard material.

During the dissolution-re-precipitation process the magnesium ions arereleased into the solution and form the magnesium hydroxide. Likewise,the vaterite transforms to the aragonite and/or the calcite through thesolution dissolution precipitation reaction. Applicants havesurprisingly found that the vaterite dissolution may need to be parallelto the dissolution of magnesium oxide for the magnesium ions to be insolution at sufficient quantity to promote the aragonite formation. Thedissolution timing can be made to coincide via controlling thesolubility and the dissolution rate of the vaterite and the magnesiumoxide (see Example 3). In some embodiments, the vaterite dissolutionrate can be modified by changing the particle size and the crystallattice. For instance, decreasing the vaterite particle size mayincrease the rate of the dissolution and the transformation. In someembodiments, inducing the crystal lattice defects may raise thesolubility of the vaterite and certain ions such as the ammonium and thesulfate ions can be further utilized to stabilize the vaterite and todecrease the dissolution rate of the vaterite. In some embodiments, themagnesium oxide dissolution rate can be affected by its size andcrystallinity. In some embodiments, the size and the properties of themagnesium oxide (under burnt, soft burnt, or dead burnt) can becontrolled by grinding and calcining (firing) conditions. In someembodiments, decreased magnesium oxide particle size, decreased firingtime, and decreased firing temperature may increase the dissolution rateof the magnesium oxide.

In one aspect, there are provided methods to form the composition,comprising:

(i) calcining the limestone to form the mixture comprising lime andmagnesium oxide, and the gaseous stream comprising carbon dioxide;

(ii) dissolving the mixture comprising lime and magnesium oxide in theN-containing salt solution to produce the aqueous solution comprisingcalcium salt and magnesium oxide;

(iii) treating the aqueous solution comprising calcium salt andmagnesium oxide with the gaseous stream comprising carbon dioxide toform the composition comprising vaterite and magnesium oxide; and

(iv) controlling average particle size of the vaterite and/orcontrolling calcining/firing temperature of the limestone and/or themagnesium bearing mineral to form the magnesium oxide and transformingthe vaterite to the aragonite and/or the calcite and transforming themagnesium oxide to the magnesium hydroxide.

In the above noted aspect, further comprising controlling the averageparticle size of the vaterite between about 1-50 micron or between 1-20micron. In the above noted aspect, further comprising controllingcalcining/firing temperature of the limestone and/or the magnesiumbearing mineral to form the lime and the magnesium oxide, to betweenabout 300° C.-1200° C.; or between about 300° C.-1000° C.; or betweenabout 300° C.-800° C.; or between about 500° C.-1000° C.

The activation of the composition comprising the vaterite and themagnesium oxide may optionally be further achieved by various otherprocesses. Various examples of the activation of the vaterite, such as,but not limited to, nuclei activation, thermal activation, mechanicalactivation, chemical activation, or combination thereof, are describedherein. In some embodiments, the vaterite is activated through variousprocesses such that aragonite and/or the calcite formation and itsmorphology and/or crystal growth can be controlled upon reaction of thevaterite containing composition with water. The aragonite and/or thecalcite formed results in higher tensile strength and fracture toleranceto the products formed from the vaterite.

In some embodiments, the vaterite may be activated by mechanical means,as described herein. For example, the composition comprising thevaterite and the magnesium oxide may be activated by creating surfacedefects on the composition such that the aragonite and/or the calciteformation is accelerated. In some embodiments, the compositioncomprising the vaterite and the magnesium oxide is a ball-milledcomposition.

The composition comprising the vaterite and the magnesium oxide may alsobe activated by providing chemical or nuclei activation to the vateritecomposition. Such chemical or nuclei activation may be provided by oneor more of aragonite seeds, calcite seeds, inorganic additive, ororganic additive. The aragonite and/or the calcite seed present in thecompositions provided herein may be obtained from natural or syntheticsources. The natural sources include, but not limited to, reef sand,lime, hard skeletal material of certain fresh-water and marineinvertebrate organisms, including pelecypods, gastropods, mollusk shell,and calcareous endoskeleton of warm- and cold-water corals, pearls,rocks, sediments, ore minerals (e.g., serpentine), and the like. Thesynthetic sources include, but not limited to, precipitated aragoniteand/or the calcite, such as formed from sodium carbonate and calciumchloride; or the aragonite and/or the calcite formed by thetransformation of the vaterite, such as transformed vaterite describedherein.

In some embodiments, the inorganic additive or the organic additive inthe compositions provided herein can be any additive that activates thevaterite. Some examples of inorganic additive or organic additive in thecompositions provided herein, include, but not limited to, sodium decylsulfate, lauric acid, sodium salt of lauric acid, urea, citric acid,sodium salt of citric acid, phthalic acid, sodium salt of phthalic acid,taurine, creatine, dextrose, poly(n-vinyl-1-pyrrolidone), aspartic acid,sodium salt of aspartic acid, magnesium chloride, acetic acid, sodiumsalt of acetic acid, glutamic acid, sodium salt of glutamic acid,strontium chloride, gypsum, lithium chloride, sodium chloride, glycine,sodium citrate dehydrate, sodium bicarbonate, magnesium sulfate,magnesium acetate, sodium polystyrene, sodium dodecylsulfonate,poly-vinyl alcohol, or combination thereof. In some embodiments,inorganic additive or organic additive in the compositions providedherein, include, but not limited to, taurine, creatine,poly(n-vinyl-1-pyrrolidone), lauric acid, sodium salt of lauric acid,urea, magnesium chloride, acetic acid, sodium salt of acetic acid,strontium chloride, magnesium sulfate, magnesium acetate, or combinationthereof. In some embodiments, inorganic additive or organic additive inthe compositions provided herein, include, but not limited to, magnesiumchloride, magnesium sulfate, magnesium acetate, or combination thereof.

In some embodiments, the inorganic additive in the compositions providedherein can be additional magnesium oxide that is externally added to thecomposition comprising the vaterite and the magnesium oxide.

Without being limited by any theory, it is contemplated that theactivation of the vaterite with the magnesium oxide and/or furtheractivation by ball-milling or by addition of the aragonite and/or thecalcite seed, the inorganic additive or the organic additive orcombination thereof may result in control of formation of the aragoniteand/or the calcite during dissolution-re-precipitation process of thevaterite including control of properties, such as, but not limited to,polymorph, morphology, particle size, cross-linking, agglomeration,coagulation, aggregation, sedimentation, crystallography, inhibitinggrowth along a certain face of a crystal, allowing growth along acertain face of a crystal, or combination thereof. For example, thepresence of the magnesium oxide and optionally other additives such asthe aragonite seed, the inorganic additive or the organic additive mayselectively target the morphology of the aragonite, inhibit the calcitegrowth and promote the formation of the aragonite that may generally notbe favorable kinetically.

In some embodiments, the one or more inorganic additives may be added tofacilitate transformation of the vaterite to the aragonite and/or thecalcite and the magnesium oxide to the magnesium hydroxide. The one ormore additives may be added during any step of the process. For example,the one or more additives may be added during contact of the aqueoussolution or the first aqueous solution with the carbon dioxide gas andoptionally the ammonia gas or the second aqueous solution; after contactof the aqueous solution or the first aqueous solution with the carbondioxide gas and optionally the ammonia gas or the second aqueoussolution; during precipitation of the composition, after precipitationof the composition in the slurry, in the slurry after the dewatering ofthe composition, in the powder after the drying of the slurry, in theaqueous solution to be mixed with the powder composition, or in theslurry made from the powdered composition with water, or any combinationthereof. In some embodiments, the water used in the process of makingthe composition may already contain the one or more additives or the oneor more additive ions. For example, if sea water is used in the process,then the additive ion may already be present in the sea water.

In some embodiments, in the foregoing methods, the amount of the one ormore additives added during the process is more than 0.1% by weight, ormore than 0.5% by weight, or more than 1% by weight, or more than 1.5%by weight, or more than 1.6% by weight, or more than 1.7% by weight, ormore than 1.8% by weight, or more than 1.9% by weight, or more than 2%by weight, or more than 2.1% by weight, or more than 2.2% by weight, ormore than 2.3% by weight, or more than 2.4% by weight, or more than 2.5%by weight, or more than 2.6% by weight, or more than 2.7% by weight, ormore than 2.8% by weight, or more than 2.9% by weight, or more than 3%by weight, or more than 3.5% by weight, or more than 4% by weight, ormore than 4.5% by weight, or more than 5% by weight, or between 0.5-5%by weight, or between 0.5-4% by weight, or between 0.5-3% by weight, or0.5-2% by weight, or 0.5-1% by weight, or 1-3% by weight, or 1-2.5% byweight, or 1-2% by weight, or 1.5-2.5% by weight, or 2-3% by weight, or2.5-3% by weight, or 0.5% by weight, or 1% by weight, or 1.5% by weight,or 2% by weight, or 2.5% by weight, or 3% by weight, or 3.5% by weight,or 4% by weight, or 4.5% by weight, or 5% by weight. In someembodiments, in the foregoing methods, the amount of the one or moreadditives added during the process is between 0.5-3% by weight orbetween 1.5-2.5% by weight.

In some embodiments, the composition comprising the vaterite and themagnesium oxide, as prepared by the methods and systems describedherein, sets and hardens (the vaterite transforms to the aragoniteand/or the calcite and the magnesium oxide to the magnesium hydroxide)after treatment with the aqueous medium under one or more suitableconditions. The aqueous medium includes, but is not limited to, freshwater optionally containing additives or brine. In some embodiments, theone or more suitable conditions include, but are not limited to,temperature, pressure, time period for setting, a ratio of the aqueousmedium to the composition, and combination thereof. The temperature maybe related to the temperature of the aqueous medium. In someembodiments, the temperature is in a range of 0-110° C.; or 0-80° C.; or0-60° C.; or 0-40° C.; or 25-100° C.; or 25-75° C.; or 25-50° C.; or37-100° C.; or 37-60° C.; or 40-100° C.; or 40-60° C.; or 50-100° C.; or50-80° C.; or 60-100° C.; or 60-80° C.; or 80-100° C.; or 100-200° C. Insome embodiments, the pressure is atmospheric pressure or above atm.pressure. In some embodiments, the time period for setting the cementproduct is 30 min. to 48 hrs; or 30 min. to 24 hrs; or 30 min. to 12hrs; or 30 min. to 8 hrs; or 30 min. to 4 hrs; or 30 min. to 2 hrs; 2 to48 hrs; or 2 to 24 hrs; or 2 to 12 hrs; or 2 to 8 hrs; or 2 to 4 hrs; 5to 48 hrs; or 5 to 24 hrs; or 5 to 12 hrs; or 5 to 8 hrs; or 5 to 4 hrs;or 5 to 2 hrs; 10 to 48 hrs; or 10 to 24 hrs; or 24 to 48 hrs.

During the mixing of the composition or the precipitation material withthe aqueous medium, the precipitate may be subjected to high shearmixer. After mixing, the precipitate may be dewatered again and placedin pre-formed molds to make formed building materials or may be used tomake formed building materials using the processes well known in the artor as described herein. Alternatively, the precipitate may be mixed withwater and may be allowed to set. The precipitate may set over a periodof days and may be then placed in the oven for drying, e.g., at 40° C.,or from 40° C.-60° C., or from 40° C.-50° C., or from 40° C.-100° C., orfrom 50° C.-60° C., or from 50° C.-80° C., or from 50° C.-100° C., orfrom 60° C.-80° C., or from 60° C.-100° C. The precipitate may besubjected to curing at high temperature, such as, from 50° C.-60° C., orfrom 50° C.-80° C., or from 50° C.-100° C., or from 60° C.-80° C., orfrom 60° C.-100° C., or 60° C., or 80° C.-100° C., or 100° C.-200° C. inhigh humidity, such as, in 30%, or 40%, or 50%, or 60%, or 100% relativehumidity.

In some embodiments of the aforementioned aspects and embodiments, thesystem further comprises a recovering system to recover the residualN-containing salt from the aqueous solution to be recycled back to thedissolution reactor. The recovering system is the system configured tocarry out thermal decomposition, reverse osmosis, multi-stage flashdistillation, multi-effect distillation, vapor recompression,distillation, and combinations thereof, as described herein above.

The methods and systems provided herein may be carried out at land(e.g., at a location close to the limestone quarry, or is easily andeconomically transported in), at sea, or in the ocean. In someembodiments, the cement plants calcining the lime may be retro-fittedwith the systems described herein to form the composition and further toform products from the composition.

Aspects include systems, including processing plants or factories, forpracticing the methods as described herein. Systems may have anyconfiguration that enables practice of the particular production methodof interest.

In certain embodiments, the systems include a source of the lime and astructure having an input for the aqueous N-containing salt solution.For example, the systems may include a pipeline or analogous feed of theaqueous N-containing salt solution, wherein the aqueous N-containingsalt solution is as described herein. The system further includes aninput for the CO₂ as well as components for combining these sources withwater (optionally an aqueous solution such as water, brine or seawater)before the precipitation or the treatment reactor or in the treatmentreactor. In some embodiments, the treatment reactor is a gas-liquidcontactor configured to contact enough CO₂ to produce the composition inexcess of 1, 10, 100, 1,000, or 10,000 tons per day.

The systems further include a treatment reactor that subjects theaqueous solution, or the first aqueous solution introduced to thetreatment reactor to the one or more precipitation conditions (asdescribed herein) and produces the composition and the supernatant. Insome embodiments, the treatment reactor is configured to hold watersufficient to produce the composition in excess of 1, 10, 100, 1,000, or10,000 tons per day. The treatment reactor may also be configured toinclude any of a number of different elements such as temperaturemodulation elements (e.g., configured to heat the water to a desiredtemperature), chemical additive elements (e.g., configured forintroducing additives etc. into the precipitation reaction mixture),computer automation, and the like.

The gaseous waste stream comprising the CO₂ and optionally the NH₃ maybe provided to the treatment reactor and/or the cooling reactor in anyconvenient manner. In some embodiments, the gaseous waste stream isprovided with a gas conveyer (e.g., a duct) that runs from thedissolution reactor to the treatment reactor and/or the cooling reactor.

Where the water source that is processed by the system to produce theprecipitation material is seawater, the input is in fluid communicationwith a source of sea water, e.g., such as where the input is a pipelineor feed from ocean water to a land-based system or an inlet port in thehull of ship, e.g., where the system is part of a ship, e.g., in anocean-based system.

The methods and systems may also include one or more detectorsconfigured for monitoring the aqueous N-containing salt solution, thelime, and/or the carbon dioxide (not illustrated in figures). Monitoringmay include, but is not limited to, collecting data about the pressure,temperature and composition of the water or the carbon dioxide gas. Thedetectors may be any convenient device configured to monitor, forexample, pressure sensors (e.g., electromagnetic pressure sensors,potentiometric pressure sensors, etc.), temperature sensors (resistancetemperature detectors, thermocouples, gas thermometers, thermistors,pyrometers, infrared radiation sensors, etc.), volume sensors (e.g.,geophysical diffraction tomography, X-ray tomography, hydroacousticsurveyers, etc.), and devices for determining chemical makeup of thewater or the carbon dioxide gas (e.g, IR spectrometer, NMR spectrometer,UV-vis spectrophotometer, high performance liquid chromatographs,inductively coupled plasma emission spectrometers, inductively coupledplasma mass spectrometers, ion chromatographs, X-ray diffractometers,gas chromatographs, gas chromatography-mass spectrometers,flow-injection analysis, scintillation counters, acidimetric titration,and flame emission spectrometers, etc.).

In some embodiments, the detectors may also include a computer interfacewhich is configured to provide a user with the collected data about theaqueous N-containing salt solution, the lime and the magnesium oxide,and/or the carbon dioxide/ammonia gas. In some embodiments, the summarymay be stored as a computer readable data file or may be printed out asa user readable document.

In some embodiments, the detector may be a monitoring device such thatit can collect real-time data (e.g., internal pressure, temperature,etc.). In other embodiments, the detector may be one or more detectorsconfigured to determine the parameters of the aqueous N-containing saltsolution, the lime, and/or the carbon dioxide and/or NH₃ gas at regularintervals, e.g., determining the composition every 1 minute, every 5minutes, every 10 minutes, every 30 minutes, every 60 minutes, every 100minutes, every 200 minutes, every 500 minutes, or some other interval.

In certain embodiments, the system may further include a station forpreparing a building material, such as cement or aggregate, from thecomposition. Other materials such as formed building materials and/ornon-cementitious materials may also be formed from the composition andappropriate station may be used for preparing the same.

As indicated above, the system may be present on land or sea. Forexample, the system may be land-based system that is in a coastalregion, e.g., close to a source of seawater, or even an interiorlocation, where water is piped into the system from a water source,e.g., ocean. Alternatively, the system is a water-based system, i.e., asystem that is present on or in water. Such a system may be present on aboat, ocean-based platform etc., as desired.

Calcium carbonate slurry is pumped via pump to the drying system, whichin some embodiments includes a filtration step followed by spray drying.The water separated from the drying system is discharged or isrecirculated to the reactor. The resultant solid or powder from thedrying system is utilized as the cement or the aggregate to produce thebuilding materials. The solid or the powder may also be used as a fillerin non-cementitious products such as paper, plastic, paint etc. Thesolid or powder may also be used in forming formed building materials,such as drywall, cement boards, etc.

In some embodiments, the systems may include a control station,configured to control the amount of the aqueous N-containing saltsolution and/or the amount of the lime conveyed to the treatment reactoror the dissolution reactor; the amount of the precipitate conveyed tothe separator; the amount of the precipitate conveyed to the dryingstation; and/or the amount of the precipitate conveyed to the refiningstation. A control station may include a set of valves or multi-valvesystems which are manually, mechanically or digitally controlled, or mayemploy any other convenient flow regulator protocol. In some instances,the control station may include a computer interface, (where regulationis computer-assisted or is entirely controlled by computer) configuredto provide a user with input and output parameters to control theamount, as described above.

II. Compositions

In one aspect, there is provided a cement or non-cement compositioncomprising the vaterite and the magnesium oxide.

As described herein, the magnesium oxide is under burnt magnesium oxide,soft burnt magnesium oxide, dead burnt magnesium oxide, or combinationsthereof.

In some embodiments of the compositions, methods, and systems aspectsprovided herein, the vaterite is partially formed on the surface of themagnesium oxide. The aforementioned embodiment may occur when the limeand the magnesium oxide go through the processes outlined in FIGS. 1-4to form the composition comprising the vaterite and the magnesium oxide.

In some embodiments, the compositions provided herein are in a powderform. In some embodiments, the compositions provided herein are in a drypowder form. In some embodiments, the compositions provided herein arewet cake compositions or slurry. In some embodiments, the compositionsprovided herein are disordered or are not in an ordered array. In stillsome embodiments, the compositions provided herein are in a partially orwholly hydrated form. In still some embodiments, the compositionsprovided herein are in saltwater or fresh water. In still someembodiments, the compositions provided herein are in water containingsodium chloride. In still some embodiments, the compositions providedherein are in water containing alkaline earth metal ions, such as, butare not limited to, calcium, magnesium, etc. In some embodiments, thecompositions provided herein are non-medical or are not for medicalprocedures.

In one aspect, there is provided the cement or the non-cement slurrycomposition comprising the vaterite, the aragonite, the calcite, themagnesium oxide, the magnesium hydroxide, or combinations thereof, andthe water. In the aforementioned aspect, the composition comprising thevaterite and the magnesium oxide, when comes in contact with the waterto form the slurry, undergoes transformation of the vaterite to thearagonite and/or the calcite (dissolution and re-precipitation in water)and the magnesium oxide to the magnesium hydroxide.

In some embodiments, the aragonite in the compositions, methods, andsystems provided herein is in shape of network of needles. In someembodiments, the magnesium hydroxide binds the aragonite needlestogether. In some embodiments, the magnesium hydroxide stabilizes thearagonite and prevents its transformation to the calcite. In someembodiments, the magnesium hydroxide binds the calcite crystalstogether. In some embodiments, the magnesium hydroxide stabilizes thecalcite.

In some embodiments, the water is bound to the composition in form ofthe magnesium hydroxide.

In some embodiments, the compositions provided herein have a pH of above10.

In some embodiments of the foregoing aspects and embodiments, thecomposition includes at least 10 wt % vaterite; or at least 20 wt %vaterite; or at least 30 wt % vaterite; or at least 40 wt % vaterite; orat least 50 wt % vaterite; or at least 60 wt % vaterite; or at least 70wt % vaterite; or at least 80 wt % vaterite; or at least 90 wt %vaterite; or at least 95 wt % vaterite; or at least 99 wt % vaterite; orfrom 10 wt % to 99 wt % vaterite; or from 10 wt % to 90 wt % vaterite;or from 10 wt % to 80 wt % vaterite; or from 10 wt % to 70 wt %vaterite; or from 10 wt % to 60 wt % vaterite; or from 10 wt % to 50 wt% vaterite; or from 10 wt % to 40 wt % vaterite; or from 10 wt % to 30wt % vaterite; or from 10 wt % to 20 wt % vaterite; or from 20 wt % to99 wt % vaterite; or from 20 wt % to 95 wt % vaterite; or from 20 wt %to 90 wt % vaterite; or from 20 wt % to 75 wt % vaterite; or from 20 wt% to 50 wt % vaterite; or from 30 wt % to 99 wt % vaterite; or from 30wt % to 95 wt % vaterite; or from 30 wt % to 90 wt % vaterite; or from30 wt % to 75 wt % vaterite; or from 30 wt % to 50 wt % vaterite; orfrom 40 wt % to 99 wt % vaterite; or from 40 wt % to 95 wt % vaterite;or from 40 wt % to 90 wt % vaterite; or from 40 wt % to 75 wt %vaterite; or from 50 wt % to 99 wt % vaterite; or from 50 wt % to 95 wt% vaterite; or from 50 wt % to 90 wt % vaterite; or from 50 wt % to 75wt % vaterite; or from 60 wt % to 99 wt % vaterite; or from 60 wt % to95 wt % vaterite; or from 60 wt % to 90 wt % vaterite; or from 70 wt %to 99 wt % vaterite; or from 70 wt % to 95 wt % vaterite; or from 70 wt% to 90 wt % vaterite; or from 80 wt % to 99 wt % vaterite; or from 80wt % to 95 wt % vaterite; or from 80 wt % to 90 wt % vaterite; or from90 wt % to 99 wt % vaterite; or 10 wt % vaterite; or 20 wt % vaterite;or 30 wt % vaterite; or 40 wt % vaterite; or 50 wt % vaterite; or 60 wt% vaterite; or 70 wt % vaterite; or 75 wt % vaterite; or 80 wt %vaterite; or 85 wt % vaterite; or 90 wt % vaterite; or 95 wt % vaterite;or 99 wt % vaterite.

In some embodiments of the foregoing aspects and embodiments, thecomposition includes between about 10-70 wt % of magnesium oxide; orbetween about 10-60 wt % of magnesium oxide; or between about 10-50 wt %of magnesium oxide; or between about 10-45 wt %; or between about 10-40wt %; or between about 10-35 wt %; or between about 10-30 wt %; orbetween about 10-25 wt %; or between about 10-20 wt %; or between about10-15 wt %; or between about 20-70 wt %; or between about 20-60 wt %; orbetween about 20-50 wt %; or between about 20-40 wt %; or between about20-30 wt %; or between about 20-25 wt %; or between about 30-70 wt %; orbetween about 30-60 wt %; or between about 30-50 wt %; or between about30-40 wt %; or between about 40-70 wt %; or between about 40-60 wt %; orbetween about 40-50 wt % of magnesium oxide in the compositions.

In some embodiments of the foregoing aspects and embodiments, thecomposition includes between about 30-99 wt % vaterite and between about1-70 wt % magnesium oxide; or between about 50-90 wt % vaterite andbetween about 10-50 wt % magnesium oxide; or between about 60-90 wt %vaterite and between about 10-40 wt % magnesium oxide; or between about70-90 wt % vaterite and between about 10-30 wt % magnesium oxide; orbetween about 80-99 wt % vaterite and between about 1-20 wt % magnesiumoxide.

In some embodiments, the composition comprising the vaterite and themagnesium oxide is a particulate composition with an average particlesize of between about 0.1-100 microns. The average particle size (oraverage particle diameter) may be determined using any conventionalparticle size determination method, such as, but not limited to,multi-detector laser scattering or laser diffraction or sieving. Incertain embodiments, unimodel or multimodal, e.g., bimodal or other,distributions are present. Bimodal distributions may allow the surfacearea to be minimized, thus allowing a lower liquids/solids mass ratiowhen composition is mixed with water yet providing smaller reactiveparticles for early reaction. In some embodiments, the composition orthe precipitation material comprising the vaterite and the magnesiumoxide provided herein is the particulate composition with an averageparticle size of 0.1-1000 microns; or 0.1-500 microns; or 0.1-100microns; or 0.1-50 microns; or 0.1-20 microns; or 0.1-10 microns; or0.1-5 microns; or 1-50 microns; or 1-25 microns; or 1-20 microns; or1-10 microns; or 1-5 microns; or 5-70 microns; or 5-50 microns; or 5-20microns; or 5-10 microns; or 10-100 microns; or 10-50 microns; or 10-20microns; or 10-15 microns; or 15-50 microns; or 15-30 microns; or 15-20microns; or 20-50 microns; or 20-30 microns; or 30-50 microns; or 40-50microns; or 50-100 microns; or 50-60 microns; or 60-100 microns; or60-70 microns; or 70-100 microns; or 70-80 microns; or 80-100 microns;or 80-90 microns; or 0.1 microns; or 0.5 microns; or 1 microns; or 2microns; or 3 microns; or 4 microns; or 5 microns; or 8 microns; or 10microns; or 15 microns; or 20 microns; or 30 microns; or 40 microns; or50 microns; or 60 microns; or 70 microns; or 80 microns; or 100 microns.For example, in some embodiments, the composition comprising thevaterite and the magnesium oxide provided herein is the particulatecomposition with an average particle size of 0.1-20 micron; or 0.1-15micron; or 0.1-10 micron; or 0.1-8 micron; or 0.1-5 micron; or 1-25micron; or 1-20 micron; or 1-15 micron; or 1-10 micron; or 1-5 micron;or 5-20 micron; or 5-10 micron. In some embodiments, the compositioncomprising the vaterite and the magnesium oxide includes two or more, orthree or more, or four or more, or five or more, or ten or more, or 20or more, or 3-20, or 4-10 different sizes of the particles in thecomposition or the precipitation material. For example, the compositionmay include two or more, or three or more, or between 3-20 particlesranging from 0.1-10 micron, 10-50 micron, 50-100 micron, 100-200 micron,200-500 micron, 500-1000 micron, and/or sub-micron sizes of theparticles. In some embodiments, the composition may have averageparticle size below 0.1 micron, or sub-micron or between 0.001 micron to1 micron or more.

In some embodiments, the composition comprising the vaterite and themagnesium oxide may further include OPC or Portland cement clinker. Theamount of Portland cement component may vary and range from 10 to 95 wt%; or 10 to 90 wt %; or 10 to 80 wt %; or 10 to 70 wt %; or 10 to 60 wt%; or 10 to 50 wt %; or 10 to 40 wt %; or 10 to 30 wt %; or 10 to 20 wt%; or 20 to 90 wt %; or 20 to 80 wt %; or 20 to 70 wt %; or 20 to 60 wt%; or 20 to 50 wt %; or 20 to 40 wt %; or 20 to 30 wt %; or 30 to 90 wt%; or 30 to 80 wt %; or 30 to 70 wt %; or 30 to 60 wt %; or 30 to 50 wt%; or 30 to 40 wt %; or 40 to 90 wt %; or 40 to 80 wt %; or 40 to 70 wt%; or 40 to 60 wt %; or 40 to 50 wt %; or 50 to 90 wt %; or 50 to 80 wt%; or 50 to 70 wt %; or 50 to 60 wt %; or 60 to 90 wt %; or 60 to 80 wt%; or 60 to 70 wt %; or 70 to 90 wt %; or 70 to 80 wt %. For example,the composition comprising the vaterite and the magnesium oxide mayinclude a blend of 75% OPC and 25% composition; or 80% OPC and 20%composition; or 85% OPC and 15% composition; or 90% OPC and 10%composition; or 95% OPC and 5% composition.

In certain embodiments, the composition comprising the vaterite and themagnesium oxide may further include the aggregate. The aggregate may beincluded in the composition or the precipitation material to provide formortars which include fine aggregate and concretes which also includecoarse aggregate. The fine aggregates are materials that almost entirelypass through a Number 4 sieve (ASTM C 125 and ASTM C 33), such as silicasand. The coarse aggregate are materials that are predominantly retainedon a Number 4 sieve (ASTM C 125 and ASTM C 33), such as silica, quartz,crushed round marble, glass spheres, granite, lime, calcite, feldspar,alluvial sands, sands or any other durable aggregate, and mixturesthereof. As such, the aggregate is used broadly to refer to a number ofdifferent types of both coarse and fine particulate material, including,but are not limited to, sand, gravel, crushed stone, slag, and recycledconcrete. The amount and nature of the aggregate may vary widely. Insome embodiments, the amount of aggregate may range from 25 to 80 wt %,such as 40 to 70 wt % and including 50 to 70 wt % of the totalcomposition made up of both the composition and the aggregate.

In some embodiments, the composition comprising the vaterite and themagnesium oxide in wet or dried form, further comprises one or moreadmixtures to impart one or more properties to the product including,but not limited to, strength, flexural strength, compressive strength,porosity, thermal conductivity, etc. The amount of admixture that isemployed may vary depending on the nature of the admixture. In someembodiments, the amount of the one or more admixtures ranges from0.01-50 wt %, such as 1-30 wt %, or 1-25 wt %, or 1-20 wt %, or 2-10 wt%. Examples of the admixtures include, but not limited to, setaccelerators, set retarders, air-entraining agents, foaming agents,defoamers, alkali-reactivity reducers, bonding admixtures, dispersants,coloring admixtures, corrosion inhibitors, damp-proofing admixtures, gasformers, permeability reducers, pumping aids, shrinkage compensationadmixtures, fungicidal admixtures, germicidal admixtures, insecticidaladmixtures, rheology modifying agents, finely divided mineraladmixtures, pozzolans, aggregates, wetting agents, strength enhancingagents, water repellents, reinforced material such as fibers, and anyother admixture. When using an admixture, the composition or theprecipitation material, to which the admixture raw materials areintroduced, is mixed for sufficient time to cause the admixture rawmaterials to be dispersed relatively uniformly throughout thecomposition.

Set accelerators may be used to accelerate the setting and earlystrength development of cement. Examples of set accelerators that may beused include, but are not limited to, POZZOLITH® NC534, non-chloridetype set accelerator and/or RHEOCRETE® CNI calcium nitrite-basedcorrosion inhibitor. Set retarding, also known as delayed-setting orhydration control, admixtures are used to retard, delay, or slow therate of setting of cement. Most set retarders may also act as low-levelwater reducers and can also be used to entrain some air into product. Anexample of a retarder is DELVO®. The air entrainer includes anysubstance that will entrain air in the compositions. Some air entrainerscan also reduce the surface tension of a composition at lowconcentration. Air-entraining admixtures are used to purposely entrainmicroscopic air bubbles into cement. Air entrainment may increase theworkability of the mix while eliminating or reducing segregation andbleeding. Materials used to achieve these desired effects can beselected from wood resin, natural resin, synthetic resin, sulfonatedlignin, petroleum acids, proteinaceous material, fatty acids, resinousacids, alkylbenzene sulfonates, sulfonated hydrocarbons, vinsol resin,anionic surfactants, cationic surfactants, nonionic surfactants, naturalrosin, synthetic rosin, an inorganic air entrainer, syntheticdetergents, and their corresponding salts, and mixtures thereof. The airentrainers are added in an amount to yield a desired level of air in acementitious composition. Examples of the air entrainers that can beutilized in the admixture system include, but are not limited to MB AE90, MB VR and MICRO AIR®, all available from BASF Admixtures Inc. ofCleveland, Ohio.

In some embodiments, the composition comprising the vaterite and themagnesium oxide further comprises foaming agent. The foaming agentsincorporate large quantities of air voids/porosity and facilitatereduction of the material's density. Examples of the foaming agentsinclude, but not limited to, soap, detergent (alkyl ether sulfate),Millifoam™ (alkyl ether sulfate), Cedepal™ (ammonium alkyl ethoxysulfate), Witcolate™ 12760, and the like.

In some embodiments, the composition comprising the vaterite and themagnesium oxide further comprises defoamers. The defoamers are used todecrease the air content in the cementitious composition. Also ofinterest as admixtures are dispersants. The dispersant includes, but isnot limited to, polycarboxylate dispersants, with or without polyetherunits. The term dispersant is also meant to include those chemicals thatalso function as a plasticizer, water reducer such as a high range waterreducer, fluidizer, anti-flocculating agent, or superplasticizer forcompositions, such as lignosulfonates, salts of sulfonated naphthalenesulfonate condensates, salts of sulfonated melamine sulfonatecondensates, beta naphthalene sulfonates, sulfonated melamineformaldehyde condensates, naphthalene sulfonate formaldehyde condensateresins for example LOMAR D® dispersant (Cognis Inc., Cincinnati, Ohio),polyaspartates, or oligomeric dispersants. Polycarboxylate dispersantscan be used, by which is meant a dispersant having a carbon backbonewith pendant side chains, wherein at least a portion of the side chainsare attached to the backbone through a carboxyl group or an ether group.

Natural and synthetic admixtures may be used to color the product foraesthetic and safety reasons. These coloring admixtures may be composedof pigments and include carbon black, iron oxide, phthalocyanine, umber,chromium oxide, titanium oxide, cobalt blue, and organic coloringagents. Also of interest as admixtures are corrosion inhibitors. Thecorrosion inhibitors may serve to protect embedded reinforcing steelfrom corrosion. The materials commonly used to inhibit the corrosion arecalcium nitrite, sodium nitrite, sodium benzoate, certain phosphates orfluorosilicates, fluoroaluminites, amines and related chemicals. Also ofinterest are damp-proofing admixtures. The damp-proofing admixturesreduce the permeability of the product that has low cement contents,high water-cement ratios, or a deficiency of fines in the aggregate.These admixtures retard moisture penetration into dry products andinclude certain soaps, stearates, and petroleum products. Also ofinterest are gas former admixtures. The gas formers, or gas-formingagents, are sometimes added to the mix to cause a slight expansion priorto hardening. The amount of expansion is dependent upon the amount ofgas-forming material used and the temperature of the fresh mixture.Aluminum powder, resin soap and vegetable or animal glue, saponin orhydrolyzed protein can be used as gas formers. Also of interest arepermeability reducers. The permeability reducers may be used to reducethe rate at which water under pressure is transmitted through the mix.Silica fume, fly ash, ground slag, natural pozzolans, water reducers,and latex may be employed to decrease the permeability of the mix.

In some embodiments, the composition comprising the vaterite and themagnesium oxide further comprises rheology modifying agent admixtures.The rheology modifying agents may be used to increase the viscosity ofthe compositions. Suitable examples of rheology modifier include firmedsilica, colloidal silica, hydroxyethyl cellulose, starch, hydroxypropylcellulose, fly ash (as defined in ASTM C618), mineral oils (such aslight naphthenic), clay such as hectorite clay, polyoxyalkylenes,polysaccharides, natural gums, or mixtures thereof. Some of the mineralextenders such as, but not limited to, sepiolite clay are rheologymodifying agents.

In some embodiments, the composition comprising the vaterite and themagnesium oxide further comprises shrinkage compensation admixtures.TETRAGUARD® is an example of a shrinkage reducing agent. Bacterial andfungal growth on or in hardened product may be partially controlledthrough the use of fungicidal and germicidal admixtures. The materialsfor these purposes include, but are not limited to, polyhalogenatedphenols, dialdrin emulsions, and copper compounds. Also of interest insome embodiments is workability improving admixtures. Entrained air,which acts like a lubricant, can be used as a workability improvingagent. Other workability agents are water reducers and certain finelydivided admixtures.

In some embodiments, the composition comprising the vaterite and themagnesium oxide further comprises reinforced material such as fibers,e.g., where fiber-reinforced product is desirable. The fibers can bemade of zirconia containing materials, aluminum, glass, steel, carbon,ceramic, grass, bamboo, wood, fiberglass, or synthetic materials, e.g.,polypropylene, polycarbonate, polyvinyl chloride, polyvinyl alcohol,nylon, polyethylene, polyester, rayon, high-strength aramid, (e.g.,Kevlar®), or mixtures thereof. The reinforced material is described inU.S. patent application Ser. No. 13/560,246, filed Jul. 27, 2012, whichis incorporated herein in its entirety in the present disclosure.

In some embodiments, the compositions provided herein further includeone or more additional components including, but are not limited to,blast furnace slag, fly ash, diatomaceous earth, and other natural orartificial pozzolans, silica fumes, limestone, gypsum, hydrated lime,air entrainers, retarders, waterproofers and coloring agents. Thesecomponents may be added to modify the properties of the cement, e.g., toprovide desired strength attainment, to provide desired setting times,etc. The amount of such components present in the composition may vary,and in certain embodiments the amounts of these components range from0.01 to 50 wt %, or 10 to 50 wt %, such as 2 to 10 wt %.

In some embodiments, the compositions provided herein further includesupplementary cementitious materials (SCM). In some embodiments, the SCMis slag, fly ash, silica fume, or calcined clay.

The components of the composition can be combined using any suitableprotocol. Each material may be mixed at the time of work, or part of orall of the materials may be mixed in advance. Alternatively, some of thematerials are mixed with water with or without admixtures, such ashigh-range water-reducing admixtures, and then the remaining materialsmay be mixed therewith. As a mixing apparatus, any conventionalapparatus can be used. For example, Hobart mixer, slant cylinder mixer,Omni Mixer, Henschel mixer, V-type mixer, and Nauta mixer can beemployed.

III. Products

Provided herein are methods and systems for utilizing the compositioncomprising the vaterite and the magnesium oxide formed from thecalcination of the limestone comprising the magnesium bearing mineralsand/or mixed with the magnesium bearing minerals, to form thecementitious and/or the non-cementitious products. Provided herein areenvironmentally friendly methods and systems of removing or separatingthe CO₂ in the gaseous waste stream from the calcination of thelimestone, and fixing the CO₂ into the non-gaseous, storage-stable form(e.g., materials for the construction of structures such as buildingsand infrastructure, as well as the structures themselves or formedbuilding materials such as drywall, or non-cementitious materials suchas paper, paint, plastic, etc. or artificial reefs) such that the CO₂does not escape into the atmosphere.

The product produced by the methods described herein may be theaggregate or the building material or a pre-cast material or a formedbuilding material. In some embodiments, the product produced by themethods described herein includes the non-cementitious materials such aspaper, paint, PVC etc. In some embodiments, the product produced by themethods described herein includes artificial reefs. These products havebeen described herein.

In one aspect, there are provided cement or non-cement productscomprising the aragonite and/or the calcite and the magnesium hydroxide.In some embodiments, the aragonite is in shape of network of needles. Insome embodiments, the magnesium hydroxide binds the aragonite and/or thecalcite together. In some embodiments, the magnesium hydroxide impartsunique characteristics to the aragonitic cement and/or the calciticcement including but not limited to, filling porosity of the aragoniteand/or the calcite making it dense and less porous; stabilizing thearagonite and preventing its transformation to the calcite; binding thearagonite needles together enhancing its strength and durability;binding the calcite together enhancing its strength and durability; andimparting a pH of above 10 to the product and preventing any steelcorrosion of the steel enforcements in the cement structures.

In some embodiments, the porosity of the product is between about 0-95%;or between about 0-90%; or between about 0-80%; or between about 0-70%;or between about 0-60%; or between about 0-50%; or between about 0-40%;or between about 0-30%; or between about 0-20%; or between about 0-10%;or between about 10-95%; or between about 10-80%; or between about10-70%; or between about 10-60%; or between about 10-50%; or betweenabout 10-40%; or between about 10-30%; or between about 10-20%; orbetween about 20-95%; or between about 20-80%; or between about 20-70%;or between about 20-60%; or between about 20-50%; or between about20-40%; or between about 20-30%; or between about 30-95%; or betweenabout 30-80%; or between about 30-70%; or between about 30-60%; orbetween about 30-50%; or between about 30-40%; or between about 50-95%;or between about 70-80%; or between about 40-70%. In some embodiments,the amount of the magnesium oxide may be optimized in the compositioncomprising the vaterite such that the porosity of the product (aftertransformation of the vaterite to the aragonite and/or the calcite andthe magnesium oxide to the magnesium hydroxide) formed from thecomposition can be optimized.

Without being limited by the methods and systems provided herein, thecomposition comprising the vaterite and the magnesium oxide may beformed by mixing the composition comprising the vaterite with themagnesium oxide where the magnesium oxide is added as an additive to thecomposition. In some embodiments, the magnesium oxide may be added tosupplement the magnesium oxide already present in the composition.

The products made from the compositions, or the precipitation materialprovided herein show one or more properties, such as, high compressivestrength, high durability, high porosity (light weight), high flexuralstrength, and less maintenance costs. In some embodiments, thecompositions comprising the vaterite and the magnesium oxide uponcombination with water, setting, and hardening, have a compressivestrength of at least 0.05 MPa (megapascal), at least 3 MPa, or at least7 MPa, or at least 10 MPa or in some embodiments, between 0.05-30 MPa,or between 3-30 MPa, or between 14-80 MPa or 14-35 MPa.

In some embodiments of the foregoing aspects and the foregoingembodiments, the composition comprising the vaterite and the magnesiumoxide after combination with water, setting, and hardening (i.e.transformation of the vaterite to the aragonite and/or the calcite andthe magnesium oxide to the magnesium hydroxide) has the compressivestrength of at least 0.05 MPa; at least 3 MPa; at least 7 MPa; at least14 MPa; or at least 16 MPa; or at least 18 MPa; or at least 20 MPa; orat least 25 MPa; or at least 30 MPa; or at least 35 MPa; or at least 40MPa; or at least 45 MPa; or at least 50 MPa; or at least 55 MPa; or atleast 60 MPa; or at least 65 MPa; or at least 70 MPa; or at least 75MPa; or at least 80 MPa; or at least 85 MPa; or at least 90 MPa; or atleast 95 MPa; or at least 100 MPa; or from 0.05-50 MPa; or from 3-50MPa; or from 3-25 MPa; or from 3-15 MPa; or from 3-10 MPa; or from 14-25MPa; or from 14-100 MPa; or from 14-80 MPa; or from 14-75 MPa; or from14-50 MPa; or from 14-25 MPa; or from 17-35 MPa; or from 17-25 MPa; orfrom 20-100 MPa; or from 20-75 MPa; or from 20-50 MPa; or from 20-40MPa; or from 30-90 MPa; or from 30-75 MPa; or from 30-60 MPa; or from40-90 MPa; or from 40-75 MPa; or from 50-90 MPa; or from 50-75 MPa; orfrom 60-90 MPa; or from 60-75 MPa; or from 70-90 MPa; or from 70-80 MPa;or from 70-75 MPa; or from 80-100 MPa; or from 90-100 MPa; or from 90-95MPa; or 14 MPa; or 3 MPa; or 7 MPa; or 16 MPa; or 18 MPa; or 20 MPa; or25 MPa; or 30 MPa; or 35 MPa; or 40 MPa; or 45 MPa. For example, in someembodiments of the foregoing aspects and the foregoing embodiments, thecomposition after setting, and hardening has a compressive strength of 3MPa to 25 MPa; or 14 MPa to 40 MPa; or 17 MPa to 40 MPa; or 20 MPa to 40MPa; or 30 MPa to 40 MPa; or 35 MPa to 40 MPa. In some embodiments, thecompressive strengths described herein are the compressive strengthsafter 1 day, or 3 days, or 7 days, or 28 days, or 56 days, or longer.

Building Material

The “building material” used herein includes material used inconstruction. In one aspect, there is provided a structure or a buildingmaterial comprising the set and hardened form of the compositioncomprising the vaterite and the magnesium oxide when the vateriteconverts to the aragonite and/or the calcite and the magnesium oxideconverts to the magnesium hydroxide that sets and hardens. In oneaspect, there is provided the structure or the building materialcomprising the aragonite and/or the calcite and the magnesium hydroxide.The product (product (A) or (B) in the FIGS. 1-3 ) containing thearagonite and/or the calcite and the magnesium hydroxide form shows oneor more unexpected properties, including but not limited to, highcompressive strength, high porosity (low density or light weight),neutral pH (e.g., useful as artificial reef), microstructure network,etc.

Examples of such structures or the building materials include, but arenot limited to, concrete, aggregate, building, driveway, foundation,kitchen slab, furniture, pavement, road, bridges, motorway, overpass,parking structure, brick, block, wall, footing for a gate, fence, orpole, and combination thereof.

Formed Building Material

The “formed building material” used herein includes materials shaped(e.g., molded, cast, cut, or otherwise produced) into structures withdefined physical shape. The formed building material may be a pre-castbuilding material, such as, a pre-cast cement or concrete product. Theformed building materials and the methods of making and using the formedbuilding materials are described in U.S. application Ser. No.12/571,398, filed Sep. 30, 2009, which is incorporated herein byreference in its entirety. The formed building materials may varygreatly and include materials shaped (e.g., molded, cast, cut, orotherwise produced) into structures with defined physical shape, i.e.,configuration. The formed building materials are distinct from amorphousbuilding materials (e.g., powder, paste, slurry, etc.) that do not havea defined and stable shape, but instead conform to the container inwhich they are held, e.g., a bag or other container. The formed buildingmaterials are also distinct from irregularly or imprecisely formedmaterials (e.g., aggregate, bulk forms for disposal, etc.) in thatformed building materials are produced according to specifications thatallow for use of formed building materials in, for example, buildings.The formed building materials may be prepared in accordance withtraditional manufacturing protocols for such structures, with theexception that the compositions provided herein are employed in makingsuch materials.

In some embodiments, the methods and systems provided herein furtherinclude setting and hardening the composition comprising the vateriteand the magnesium oxide where the vaterite converts to the aragoniteand/or the calcite and the magnesium oxide converts to the magnesiumhydroxide, that sets and hardens and forms a formed building material.In one aspect, there is provided the formed building material comprisingthe aragonite and/or the calcite and the magnesium hydroxide.

In some embodiments, the formed building materials made from thecomposition comprising the vaterite and the magnesium oxide have acompressive strength or the flexural strength of at least 0.05 MPa, atleast 3 MPa, at least 10 MPa, or at least 14 MPa, or between 3-30 MPa,or between about 14-100 MPa, or between about 14-45 MPa; or thecompressive strength of the composition after setting, and hardening, asdescribed herein.

Examples of the formed building materials that can be produced by theforegoing methods and systems, include, but not limited to, masonryunits, for example only, bricks, blocks, and tiles including, but notlimited to, ceiling tiles; construction panels, for example only, cementboard (boards traditionally made from cement such as fiber cement board)and/or drywall (boards traditionally made from gypsum); conduits;basins; beam; column, slab; acoustic barrier; insulation material; orcombinations thereof. Construction panels are formed building materialsemployed in a broad sense to refer to any non-load-bearing structuralelement that are characterized such that their length and width aresubstantially greater than their thickness. As such the panel may be aplank, a board, shingles, and/or tiles. Exemplary construction panelsformed from the precipitation material provided herein include cementboards and/or drywall. Construction panels are polygonal structures withdimensions that vary greatly depending on their intended use. Thedimensions of construction panels may range from 50 to 500 cm in length,including 100 to 300 cm, such as 250 cm; width ranging from 25 to 200cm, including 75 to 150 cm, such as 100 cm; thickness ranging from 5 to25 mm, including 7 to 20 mm, including 10 to 15 mm.

In some embodiments, the cement board and/or the drywall may be used inmaking different types of boards such as, but not limited to,paper-faced board (e.g. surface reinforcement with cellulose fiber),fiberglass-faced or glass mat-faced board (e.g., surface reinforcementwith glass fiber mat), fiberglass mesh reinforced board (e.g. surfacereinforcement with glass mesh), and/or fiber-reinforced board (e.g.,cement reinforcement with cellulose, glass, fiber etc.). These boardsmay be used in various applications including, but not limited to,sidings such as, fiber-cement sidings, roofing, soffit, sheathing,cladding, decking, ceiling, shaft liner, wall board, backer, trim,frieze, shingle, and fascia, and/or underlayment.

The cement boards made by the methods and systems provided herein aremade from the composition comprising the vaterite and the magnesiumoxide that partially or wholly replaces the traditional cement in theboard. In some embodiments, the cement boards may comprise constructionpanels prepared as a combination of the aragonitic and the magnesiumhydroxide cement or a combination of the calcitic and the magnesiumhydroxide cement and fiber and/or fiberglass and may possess additionalfiber and/or fiberglass reinforcement at both faces of the board.

The cement boards are formed building materials which in someembodiments, are used as backer boards for ceramics that may be employedbehind bathroom tiles, kitchen counters, backsplashes, etc. and may havelengths ranging from 100 to 200 cm. The cement boards may vary inphysical and mechanical properties. In some embodiments, the flexuralstrength may vary, ranging between 1 to 7.5 MPa, including 2 to 6 MPa,such as 5 MPa. The compressive strengths may also vary, ranging from 5to 50 MPa, including 10 to 30 MPa, such as 15 to 20 MPa. In someembodiments, the cement boards may be employed in environments havingextensive exposure to moisture (e.g., commercial saunas). Thecomposition or the precipitation material described herein may be usedto produce the desired shape and size to form the cement board. Inaddition, a variety of further components may be added to the cementboards which include, but are not limited to, plasticizers, clay,foaming agents, accelerators, retarders and air entrainment additives.The composition is then poured out into sheet molds or a roller may beused to form sheets of a desired thickness. The shaped composition maybe further compacted by roller compaction, hydraulic pressure,vibrational compaction, or resonant shock compaction. The sheets arethen cut to the desired dimensions of the cement boards.

Another type of construction panel formed from the composition describedherein is backer board. The backer board may be used for theconstruction of interior, and/or exterior floors, walls and ceilings. Inthe embodiments, the backer board is made partially or wholly from thecomposition comprising the vaterite and the magnesium oxide.

Another type of construction panel formed from the compositions isdrywall. The drywall includes board that is used for construction ofinterior, and/or exterior floors, walls and ceilings. Traditionally, thedrywall is made from gypsum (called paper-faced board). In theembodiments, the drywall is made partially or wholly from thecomposition comprising the vaterite and the magnesium oxide therebyreplacing gypsum from the drywall product. In some embodiments, thedrywall may comprise construction panels prepared as a combination ofthe aragonitic and/or the calcitic and the magnesium hydroxide cementand cellulose, fiber and/or fiberglass and may possess additional paper,fiber, fiberglass mesh and/or fiberglass mat reinforcement at both facesof the board. Various processes for making the drywall product are wellknown in the art and are well within the scope of the invention. Someexamples include, but not limited to, wet process, semi dry process,extrusion process, Wonderborad® process, etc., that have been describedherein.

In some embodiments, the drywall is panel made of a paper liner wrappedaround an inner core. For example, in some embodiments, during theprocess of making the drywall product from the composition comprisingthe vaterite and the magnesium oxide, the slurry of the compositioncomprising the vaterite and the magnesium oxide is poured over a sheetof paper. Another sheet of paper is then put on top of the compositionsuch that the composition is flanked by the paper on both sides (theresultant composition sandwiched between two sheets of outer material,e.g., heavy paper or fiberglass mats). The vaterite in the compositionthen transforms to the aragonite and/or the calcite and the magnesiumoxide transforms to the magnesium hydroxide (optionally using heat)which then sets and hardens. When the core sets and is dried in a largedrying chamber, the sandwich becomes rigid and strong enough for use asthe building material. The drywall sheets are then cut and separated.

The flexural and the compressive strengths of the drywall formed fromthe composition comprising the vaterite and the magnesium oxide areequal to or higher than conventional drywall prepared with gypsumplaster, which is known to be a soft construction material. In someembodiments, the flexural strength may range between 0.1 to 3 MPa,including 0.5 to 2 MPa, such as 1.5 MPa. The compressive strengths mayalso vary, in some instances ranging from 1 to 20 MPa, including 5 to 15MPa, such as 8 to 10 MPa. In some embodiments, the formed buildingmaterials such as, the construction panels such as, but not limited to,the cement boards and the drywall produced by the methods and systemsdescribed herein, have low density and high porosity making themsuitable for lightweight and insulation applications. The high porosityand light weight of the formed building materials such as theconstruction panels may be due to the development of the aragoniticand/or the calcitic microstructure when the vaterite transforms to thearagonite and/or the calcite and filling of the porosity of thearagonite and/or the calcite with the magnesium hydroxide. Thetransformation of the vaterite during dissolution/re-precipitationprocess may lead to micro porosity generation while at the same time thevoids created between the aragonitic crystals and/or the calcite formedmay be filled with the magnesium hydroxide providing strength and lightweight structure. Certain admixtures may be added during thetransformation process such as, but not limited to, the foaming agents,the rheology modifiers and the mineral extenders, such as, but notlimited to, clay, starch, etc. which may add to the porosity in theproduct as the foaming agent may entrain air in the mixture and lowerthe overall density and mineral extender such as sepiolite clay mayincrease the viscosity of the mixture thereby preventing segregation ofthe composition and water.

One of the applications of the cement board or the drywall is the fibercement siding. The fiber-cement sidings formed by the methods andsystems provided herein comprise construction panels prepared as acombination of the aragonitic cement and/or the calcitic cement,aggregate, interwoven cellulose, and/or polymeric fibers and may possessa texture and flexibility that resembles wood.

In some embodiments, the formed building materials are masonry units.The masonry units are formed building materials used in the constructionof load-bearing and non-load-bearing structures that are generallyassembled using mortar, grout, and the like. Exemplary masonry unitsformed from the compositions include bricks, blocks, and tiles.

Another formed building material formed from the compositions describedherein is a conduit. The conduits are tubes or analogous structuresconfigured to convey a gas or liquid, from one location to another. Theconduits can include any of a number of different structures used in theconveyance of a liquid or gas that include, but are not limited to,pipes, culverts, box culverts, drainage channels and portals, inletstructures, intake towers, gate wells, outlet structures, and the like.

Another formed building material formed from the compositions describedherein is basins. The term basin may include any configured containerused to hold a liquid, such as water. As such, the basin may include,but is not limited to structures such as wells, collection boxes,sanitary manholes, septic tanks, catch basins, grease traps/separators,storm drain collection reservoirs, etc.

Another formed building material formed from the compositions describedherein is a beam, which, in a broad sense, refers to a horizontalload-bearing structure possessing large flexural and compressivestrengths. The beams may be rectangular cross-shaped, C-channel,L-section edge beams, I-beams, spandrel beams, H-beams, possess aninverted T-design, etc. The beams may also be horizontal load-bearingunits, which include, but are not limited to joists, lintels, archwaysand cantilevers.

Another formed building material formed from the compositions describedherein is a column, which, in a broad sense, refers to a verticalload-bearing structure that carries loads chiefly through axialcompression and includes structural elements such as compressionmembers. Other vertical compression members of the invention mayinclude, but are not limited to pillars, piers, pedestals, or posts.

Another formed building material formed from the compositions describedherein is a concrete slab. The concrete slabs are those buildingmaterials used in the construction of prefabricated foundations, floorsand wall panels. In some instances, the concrete slab may be employed asa floor unit (e.g., hollow plank unit or double tee design).

Another formed building material formed from the compositions describedherein is an acoustic barrier, which refers to a structure used as abarrier for the attenuation or absorption of sound. As such, theacoustic barrier may include, but is not limited to, structures such asacoustical panels, reflective barriers, absorptive barriers, reactivebarriers, etc.

Another formed building material formed from the compositions describedherein is an insulation material, which refers to a material used toattenuate or inhibit the conduction of heat. Insulation may also includethose materials that reduce or inhibit radiant transmission of heat.

In some embodiments, the other formed building materials such aspre-cast concrete products include, but not limited to, bunker silo;cattle feed bunk; cattle grid; agricultural fencing; H-bunks; J-bunks;livestock slats; livestock watering troughs; architectural panel walls;cladding (brick); building trim; foundation; floors, including slab ongrade; walls; double wall precast sandwich panel; aqueducts;mechanically stabilized earth panels; box culverts; 3-sided culverts;bridge systems; RR crossings; RR ties; sound walls/barriers; Jerseybarriers; tunnel segments; reinforced concrete box; utility protectionstructure; hand holes; hollowcore product; light pole base; meter box;panel vault; pull box; telecom structure; transformer pad; transformervault; trench; utility vault; utility pole; controlled environmentvaults; underground vault; mausoleum; grave stone; coffin; haz matstorage container; detention vaults; catch basins; manholes; aerationsystem; distribution box; dosing tank; dry well; grease interceptor;leaching pit; sand-oil/oil-water interceptor; septic tank; water/sewagestorage tank; wetwells; fire cisterns; floating dock; underwaterinfrastructure; decking; railing; sea walls; roofing tiles; pavers;community retaining wall; res. retaining wall; modular block systems;and segmental retaining walls.

Non-Cementitious Compositions

In some embodiments, the methods and systems described herein includemaking other products from the compositions described herein including,but not limited to, non-cementitious compositions including paper,polymer product, lubricant, adhesive, rubber product, chalk, asphaltproduct, paint, abrasive for paint removal, personal care product,cosmetic, cleaning product, personal hygiene product, ingestibleproduct, agricultural product, soil amendment product, pesticide,environmental remediation product, and combination thereof. Suchcompositions have been described in U.S. Pat. No. 7,829,053, issued Nov.9, 2010, which is incorporated herein by reference in its entirety.

Artificial Marine Structures

In some embodiments, the methods described herein include makingartificial marine structures from the compositions described hereinincluding, but not limited to, artificial corals and reefs. In someembodiments, the artificial structures can be used in the aquariums orsea. In some embodiments, these products are made from the compositionscomprising the vaterite and the magnesium oxide that transforms to thearagonite and/or the calcite and the magnesium hydroxide, after settingand hardening. The aragonitic cement and/or the calcitic cement mayprovide neutral or close to neutral pH which may be conducive formaintenance and growth of marine life. The aragonitic reefs may providesuitable habitat for marine species.

Throughout the description, where compositions are described as having,including, or comprising specific components, or where processes andmethods are described as having, including, or comprising specificsteps, it is contemplated that, additionally, there are compositions ofthe present invention that consist essentially of, or consist of, therecited components, and that there are processes and methods accordingto the present invention that consist essentially of, or consist of, therecited processing steps.

In the application, where an element or component is said to be includedin and/or selected from a list of recited elements or components, itshould be understood that the element or component can be any one of therecited elements or components, or the element or component can beselected from a group consisting of two or more of the recited elementsor components.

Further, it should be understood that elements and/or features of acomposition or a method described herein can be combined in a variety ofways without departing from the spirit and scope of the presentinvention, whether explicit or implicit herein. For example, wherereference is made to a particular composition, that composition can beused in various embodiments of compositions of the present inventionand/or in methods of the present invention, unless otherwise understoodfrom the context. In other words, within this application, embodimentshave been described and depicted in a way that enables a clear andconcise application to be written and drawn, but it is intended and willbe appreciated that embodiments may be variously combined or separatedwithout parting from the present teachings and invention(s). Forexample, it will be appreciated that all features described and depictedherein can be applicable to all aspects of the invention(s) describedand depicted herein.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the invention, subject toany specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

The use of the term “include,” “includes,” “including,” “have,” “has,”“having,” “contain,” “contains,” or “containing,” including grammaticalequivalents thereof, should be understood generally as open-ended andnon-limiting, for example, not excluding additional unrecited elementsor steps, unless otherwise specifically stated or understood from thecontext.

Certain ranges are presented herein with numerical values being precededby the term “about.” The term “about” is used herein to provide literalsupport for the exact number that it precedes, as well as a number thatis near to or approximately the number that the term precedes. As usedherein, the term “about” refers to a ±10% variation from the nominalvalue unless otherwise indicated or inferred.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the invention, representativeillustrative methods and materials are described herein.

All publications, patents, and patent applications cited in thisspecification are incorporated herein by reference to the same extent asif each individual publication, patent, or patent application werespecifically and individually indicated to be incorporated by reference.Furthermore, each cited publication, patent, or patent application isincorporated herein by reference to disclose and describe the subjectmatter in connection with which the publications are cited. The citationof any publication is for its disclosure prior to the filing date andshould not be construed as an admission that the invention describedherein is not entitled to antedate such publication by virtue of priorinvention. Further, the dates of publication provided may be differentfrom the actual publication dates, which may need to be independentlyconfirmed.

It should be understood that the expression “at least one of” includesindividually each of the recited objects after the expression and thevarious combinations of two or more of the recited objects unlessotherwise understood from the context and use.

It is noted that, as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural references unless thecontext clearly dictates otherwise. It is further noted that the claimsmay be drafted to exclude any optional element. As such, this statementis intended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only” and the like in connection with therecitation of claim elements, or use of a “negative” limitation.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the invention.Any recited method can be carried out in the order of events recited orin any other order, which is logically possible. It should be understoodthat the order of steps or order for performing certain actions isimmaterial so long as the present invention remain operable. Moreover,two or more steps or actions may be conducted simultaneously.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the invention and are not intended to limit the scope ofwhat the inventors regard as their invention nor are they intended torepresent that the experiments below are all or the only experimentsperformed. Efforts have been made to ensure accuracy with respect tonumbers used (e.g., amounts, temperature, etc.) but some experimentalerrors and deviations should be accounted for.

EXAMPLES Example 1 Formation and Transformation of Vaterite andMagnesium Oxide

NH₄Cl was dissolved into water. Lime containing magnesium oxide wasadded to the aqueous solution and mixed at 30° C. in a vessel. Theprecipitation reactor was an acrylic cylinder equipped with baffles, pHelectrode, thermocouple, turbine impeller, and inlet and outlet portsfor liquid feeds and product slurry. During startup, theCaCl₂-containing solution was pumped into the reactor and a 4:1 N₂:CO₂gas mixture was sparged into the reactor until the desired pH wasreached. After achieving the desired pH, the CaCl₂-containing solutionwas pumped into the reactor at a fixed flow rate. The mixture wasstirred continuously. The vaterite and the magnesium oxide slurry wereformed and were removed from the top of the reactor. The resultantvaterite and the magnesium oxide slurry were continuously collected intoa holding container. The collected slurry was periodically vacuumfiltered. The vaterite and the magnesium oxide filter cake was ovendried at 100° C. The cake showed 74% vaterite, 1% calcite, and 25%periclase via X-ray diffraction with a median particle size of 13.1microns. The clear filtrate containing regenerated NH₄Cl was recycled insubsequent experiments.

The dried vaterite and the magnesium oxide powder was mixed with waterinto a paste. The paste was cured at 80° C. and 98% relative humidity.After 1 day the hardened paste was removed from the curing environmentand dried at 100° C. XRD analysis of the hardened paste showed 1%vaterite, 65% aragonite, 1% calcite, 1% periclase, and 32% brucite.

Example 2 Formation and Transformation of Vaterite and Magnesium Oxide

This Experiment demonstrated that the hydration of the magnesium oxideto form the magnesium hydroxide increased the volume of the solidfraction of the cement paste (vaterite transformed to aragonite) bychemically binding water, whereas the transformation of the vaterite tothe aragonite (in the absence of the magnesium oxide) resulted in adecrease in the volume of the cement paste because the aragonite isdenser than the vaterite. Table 2 compares the solid volume of a (a)pure calcium carbonate cement paste to (b) a calcium carbonate cementpaste that contained 25% magnesium oxide. Table 2 below shows that thevaterite, periclase (MgO) and water formed the cement paste which aftersetting and hardening formed aragonite and brucite (Mg(OH)₂). The waterin the paste (b) bound to the Mg(OH)₂ after setting and hardening of thecement. Replacing 25% vaterite with magnesium oxide resulted in a 20%increase in the solid volume of the hardened cement, which means thatthe cement had lower porosity and higher strength, hardness, anddurability compared to a 100% calcium carbonate cement paste.

TABLE 2 Peri- Ara- Change Cement Property Vaterite clase Water Totalgonite Brucite Water Total (%) Density 2.5 3.6 1.0 2.9 2.4 1.0 (g/cm³)a) Mass (g) 100.0 0.0 30.0 100.0 0.0 30.0 Solid 39.4 0.0 39.4 34.0 0.034.0 −13.6% Volume (cm³) b) Mass (g) 75.0 25.0 30.0 75.0 36.2 18.8 Solid29.5 7.0 36.5 25.5 15.1 40.6   11.3% Volume (cm³)

FIGS. 6-7 show the microstructural differences between the calciumcarbonate cement made from the vaterite (FIGS. 6A-6B) and the calciumcarbonate cement made from the vaterite and the magnesium oxide (FIGS.7A-7B). In FIGS. 6A-B, the interconnected aragonite network of thecalcium carbonate cement can be seen. In FIGS. 7A-7B, the magnesiumhydroxide can be seen surrounding the aragonite network which helped tofill the porosity of the aragonite network and bind the aragoniteneedles together resulting in lower porosity and higher strength,hardness, and durability.

Example 3 Controlling Vaterite Transformation to Aragonite byControlling MgO Firing Temperature

Vaterite with a 4 μm median size was combined at a ratio of 4:1 withmagnesium oxide that had been separately fired. The magnesium oxide wasproduced by firing magnesium hydroxide for 4 hours at either 750° C. or950° C. A cement paste was formed by mixing the vaterite/magnesium oxidemixture with water at a water to solids ratio of 0.6. The paste was thencured in a sealed container at 80° C. for 24 hours. After curing, thepaste was dried at 110° C., then analyzed via X-ray diffraction. Table 3shows the X-ray diffraction results of the paste transformation study.As shown in Table 3, the 4 μm vaterite in combination with the lightlyburned magnesium oxide (at 750° C.) had sufficient rate of dissolutionof the magnesium ions to control the transformation of the vaterite tothe aragonite. In contrast, the magnesium oxide burned at 950° C., didnot dissolve readily enough and the vaterite transformed to the calcite.

TABLE 2 Order Rectangular pulse train amplitude vector 2 1 −1 0 0 0 0 00 0 0 3 1 −2 1 0 0 0 0 0 0 0 4 1 −3 3 −1 0 0 0 0 0 0 5 1 −4 6 −4 1 0 0 00 0 6 1 −5 10 −10 5 −1 0 0 0 0 7 1 −6 15 −20 15 −6 1 0 0 0 8 1 −7 21 −3535 −21 7 −1 0 0 9 1 −8 28 −56 70 −56 28 −8 1 0 10 1 −9 36 −84 126 −12684 −36 9 −1

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it should be readily apparent to those of ordinary skillin the art in light of the teachings of this invention that certainchanges and modifications may be made thereto without departing from thespirit or scope of the appended claims. Accordingly, the precedingmerely illustrates the principles of the invention. It will beappreciated that those skilled in the art will be able to devise variousarrangements, which, although not explicitly described or shown herein,embody the principles of the invention, and are included within itsspirit and scope. Furthermore, all examples and conditional languagerecited herein are principally intended to aid the reader inunderstanding the principles of the invention and the conceptscontributed by the inventors to furthering the art and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the invention,therefore, is not intended to be limited to the exemplary embodimentsshown and described herein. It is intended that the following claimsdefine the scope of the invention and that methods and structures withinthe scope of these claims and their equivalents be covered thereby.

What is claimed is:
 1. A cement or non-cement composition comprisingvaterite and magnesium oxide, wherein the vaterite is between about30-90 wt % and magnesium oxide is between about 1-70 wt % and/orparticle size of the vaterite is between about 0.1-100 micron.
 2. Thecomposition of claim 1, wherein the composition is a slurry compositionfurther comprising aragonite, magnesium hydroxide, and water, whereinthe aragonite is in shape of network of needles.
 3. The composition ofclaim 2, wherein the magnesium hydroxide is bound with the aragoniteneedles.
 4. The composition of claim 1, further comprising admixture,aggregate, additive, Portland cement clinker, supplementary cementitiousmaterial (SCM), or combination thereof.
 5. The composition of claim 1,wherein the magnesium oxide is under burnt magnesium oxide, soft burntmagnesium oxide, dead burnt magnesium oxide, or combination thereof. 6.The composition of claim 1, wherein the composition is a dry powdercomposition, wet cake composition, or slurry.
 7. A method to form acomposition, comprising: (i) calcining limestone to form a mixturecomprising lime and magnesium oxide, and a gaseous stream comprisingcarbon dioxide; (ii) dissolving the mixture comprising lime andmagnesium oxide in a N-containing salt solution to produce an aqueoussolution comprising calcium salt and a solid comprising magnesium oxide;(iii) treating the aqueous solution comprising calcium salt and thesolid comprising magnesium oxide with the gaseous stream comprisingcarbon dioxide to form a composition comprising vaterite and the solidcomprising magnesium oxide, and (iv) transforming the vaterite toaragonite and/or calcite upon dissolution and re-precipitation in waterand transforming the magnesium oxide to magnesium hydroxide.
 8. Themethod of claim 7, wherein the solid comprising magnesium oxide isseparated from the aqueous solution before the treating step and mixedin the composition comprising vaterite after the treating step.
 9. Themethod of claim 7, wherein the limestone comprises magnesium ormagnesium bearing mineral and/or wherein the method further comprisesmixing a magnesium bearing mineral with the limestone before thecalcination.
 10. The method of claim 9, wherein the magnesium bearingmineral comprises magnesium carbonate, magnesium salt, magnesiumhydroxide, magnesium silicate, magnesium sulfate, or combinationthereof.
 11. The method of claim 7, wherein the calcining produces amixture comprising under burnt lime, soft burnt lime, dead burnt lime,under burnt magnesium oxide, soft burnt magnesium oxide, dead burntmagnesium oxide, or combination thereof.
 12. The method of claim 7,wherein the aragonite is in shape of network of needles and the methodfurther comprises binding the aragonite needles together with themagnesium hydroxide and/or the method further comprises filling porosityof the aragonite and/or the calcite with the magnesium hydroxide makingit dense and less porous.
 13. The method of claim 7, wherein theN-containing salt is selected from the group consisting of N-containinginorganic salt, N-containing organic salt, and combination thereof. 14.The method of claim 13, wherein the N-containing inorganic salt isselected from the group consisting of ammonium halide, ammonium acetate,ammonium sulfate, ammonium sulfite, ammonium nitrate, ammonium nitrite,and combination thereof.
 15. The method of claim 7, wherein the aqueoussolution further comprises ammonia.
 16. The method of claim 7, whereinthe aragonite and/or the calcite sets and hardens to form buildingmaterial, formed building material, non-cementitious product, and/orartificial marine structure.
 17. The method of claim 7, furthercomprising adding an additive to the aqueous solution and/or to thecomposition, wherein the additive is selected from the group consistingof fatty acid ester, sodium decyl sulfate, lauric acid, sodium salt oflauric acid, urea, citric acid, sodium salt of citric acid, phthalicacid, sodium salt of phthalic acid, taurine, creatine, dextrose,poly(n-vinyl-1-pyrrolidone), aspartic acid, sodium salt of asparticacid, magnesium chloride, acetic acid, sodium salt of acetic acid,glutamic acid, sodium salt of glutamic acid, strontium chloride, gypsum,lithium chloride, sodium chloride, glycine, sodium citrate dehydrate,sodium bicarbonate, magnesium sulfate, magnesium acetate, sodiumpolystyrene, sodium dodecylsulfonate, poly-vinyl alcohol, andcombination thereof.
 18. The method of claim 7, further comprisingblending the composition with aggregate, Portland cement clinker,supplementary cementitious material (SCM), or combination thereof. 19.The method of claim 7, further comprising mixing the composition with anadmixture selected from the group consisting of set accelerator, setretarder, air-entraining agent, foaming agent, defoamer,alkali-reactivity reducer, bonding admixture, dispersant, coloringadmixture, corrosion inhibitor, damp-proofing admixture, gas former,permeability reducer, pumping aid, shrinkage compensation admixture,fungicidal admixture, germicidal admixture, insecticidal admixture,rheology modifying agent, finely divided mineral admixture, pozzolan,aggregate, wetting agent, strength enhancing agent, water repellent,reinforced material, and combination thereof.
 20. The method of claim19, wherein the reinforced material is a fiber made of zirconia,aluminum, glass, steel, carbon, ceramic, grass, bamboo, wood,fiberglass, synthetic material, or combination thereof.
 21. The methodof claim 20, wherein the synthetic material comprises polypropylene,polycarbonate, polyvinyl chloride, polyvinyl alcohol, nylon,polyethylene, polyester, rayon, high-strength aramid, or mixturethereof.